Enable building contrib/xml2 if configured using --with-libxml.

If this breaks things due to missing libxslt, then I'll have to
revert it, but let's see if it breaks the buildfarm.

Workarounds in case libxslt is missing include:
. don't configure with libxml, or
. don't build contrib modules from the contrib Makefile (use the individual module Makefiles instead), or
. change the xml2 Makefile

configure

@@ -314,7 +314,7 @@ ac_includes_default="\
 # include <unistd.h>
 #endif"
 
-ac_subst_vars='SHELL PATH_SEPARATOR PACKAGE_NAME PACKAGE_TARNAME PACKAGE_VERSION PACKAGE_STRING PACKAGE_BUGREPORT exec_prefix prefix program_transform_name bindir sbindir libexecdir datadir sysconfdir sharedstatedir localstatedir libdir includedir oldincludedir infodir mandir build_alias host_alias target_alias DEFS ECHO_C ECHO_N ECHO_T LIBS configure_args build build_cpu build_vendor build_os host host_cpu host_vendor host_os PORTNAME docdir enable_nls WANTED_LANGUAGES default_port enable_shared enable_rpath enable_debug enable_profiling DTRACE DTRACEFLAGS enable_dtrace CC CFLAGS LDFLAGS CPPFLAGS ac_ct_CC EXEEXT OBJEXT CPP GCC TAS autodepend INCLUDES enable_thread_safety with_tcl with_perl with_python with_krb5 krb_srvtab with_pam with_ldap with_bonjour with_openssl XML2_CONFIG with_zlib EGREP ELF_SYS LDFLAGS_SL AWK FLEX FLEXFLAGS LN_S LD with_gnu_ld ld_R_works RANLIB ac_ct_RANLIB TAR STRIP ac_ct_STRIP STRIP_STATIC_LIB STRIP_SHARED_LIB YACC YFLAGS PERL perl_archlibexp perl_privlibexp perl_useshrplib perl_embed_ldflags PYTHON python_version python_configdir python_includespec python_libdir python_libspec python_additional_libs HAVE_IPV6 LIBOBJS acx_pthread_config PTHREAD_CC PTHREAD_LIBS PTHREAD_CFLAGS LDAP_LIBS_FE LDAP_LIBS_BE HAVE_POSIX_SIGNALS MSGFMT MSGMERGE XGETTEXT localedir TCLSH TCL_CONFIG_SH TCL_INCLUDE_SPEC TCL_LIB_FILE TCL_LIBS TCL_LIB_SPEC TCL_SHARED_BUILD TCL_SHLIB_LD_LIBS NSGMLS JADE have_docbook DOCBOOKSTYLE COLLATEINDEX SGMLSPL vpath_build LTLIBOBJS'
+ac_subst_vars='SHELL PATH_SEPARATOR PACKAGE_NAME PACKAGE_TARNAME PACKAGE_VERSION PACKAGE_STRING PACKAGE_BUGREPORT exec_prefix prefix program_transform_name bindir sbindir libexecdir datadir sysconfdir sharedstatedir localstatedir libdir includedir oldincludedir infodir mandir build_alias host_alias target_alias DEFS ECHO_C ECHO_N ECHO_T LIBS configure_args build build_cpu build_vendor build_os host host_cpu host_vendor host_os PORTNAME docdir enable_nls WANTED_LANGUAGES default_port enable_shared enable_rpath enable_debug enable_profiling DTRACE DTRACEFLAGS enable_dtrace CC CFLAGS LDFLAGS CPPFLAGS ac_ct_CC EXEEXT OBJEXT CPP GCC TAS autodepend INCLUDES enable_thread_safety with_tcl with_perl with_python with_krb5 krb_srvtab with_pam with_ldap with_bonjour with_openssl XML2_CONFIG with_libxml with_zlib EGREP ELF_SYS LDFLAGS_SL AWK FLEX FLEXFLAGS LN_S LD with_gnu_ld ld_R_works RANLIB ac_ct_RANLIB TAR STRIP ac_ct_STRIP STRIP_STATIC_LIB STRIP_SHARED_LIB YACC YFLAGS PERL perl_archlibexp perl_privlibexp perl_useshrplib perl_embed_ldflags PYTHON python_version python_configdir python_includespec python_libdir python_libspec python_additional_libs HAVE_IPV6 LIBOBJS acx_pthread_config PTHREAD_CC PTHREAD_LIBS PTHREAD_CFLAGS LDAP_LIBS_FE LDAP_LIBS_BE HAVE_POSIX_SIGNALS MSGFMT MSGMERGE XGETTEXT localedir TCLSH TCL_CONFIG_SH TCL_INCLUDE_SPEC TCL_LIB_FILE TCL_LIBS TCL_LIB_SPEC TCL_SHARED_BUILD TCL_SHLIB_LD_LIBS NSGMLS JADE have_docbook DOCBOOKSTYLE COLLATEINDEX SGMLSPL vpath_build LTLIBOBJS'
 ac_subst_files=''
 
 # Initialize some variables set by options.
@@ -4331,6 +4331,7 @@ done
 fi
 
 
+
 #
 # Zlib
 #
@@ -24320,6 +24321,7 @@ s,@with_ldap@,$with_ldap,;t t
 s,@with_bonjour@,$with_bonjour,;t t
 s,@with_openssl@,$with_openssl,;t t
 s,@XML2_CONFIG@,$XML2_CONFIG,;t t
+s,@with_libxml@,$with_libxml,;t t
 s,@with_zlib@,$with_zlib,;t t
 s,@EGREP@,$EGREP,;t t
 s,@ELF_SYS@,$ELF_SYS,;t t

configure.in

 dnl Process this file with autoconf to produce a configure script.
-dnl $PostgreSQL: pgsql/configure.in,v 1.509 2007/04/06 05:36:50 tgl Exp $
+dnl $PostgreSQL: pgsql/configure.in,v 1.510 2007/04/13 18:50:01 adunstan Exp $
 dnl
 dnl Developers, please strive to achieve this order:
 dnl
@@ -577,6 +577,7 @@ if test "$with_libxml" = yes ; then
   fi
 fi
 
+AC_SUBST(with_libxml)
 
 #
 # Zlib

contrib/Makefile

-# $PostgreSQL: pgsql/contrib/Makefile,v 1.71 2007/02/08 15:09:47 momjian Exp $
+# $PostgreSQL: pgsql/contrib/Makefile,v 1.72 2007/04/13 18:50:01 adunstan Exp $
 
 subdir = contrib
 top_builddir = ..
@@ -37,9 +37,12 @@ ifeq ($(with_openssl),yes)
 WANTED_DIRS += sslinfo
 endif
 
+ifeq ($(with_libxml),yes)
+WANTED_DIRS += xml2
+endif
+
 # Missing:
 #		start-scripts	\ (does not have a makefile)
-#		xml2		\ (requires libxml installed)
 
 
 all install installdirs uninstall distprep clean distclean maintainer-clean:

src/Makefile.global.in

 # -*-makefile-*-
-# $PostgreSQL: pgsql/src/Makefile.global.in,v 1.233 2007/02/09 15:55:57 petere Exp $
+# $PostgreSQL: pgsql/src/Makefile.global.in,v 1.234 2007/04/13 18:50:01 adunstan Exp $
 
 #------------------------------------------------------------------------------
 # All PostgreSQL makefiles include this file and use the variables it sets,
@@ -152,6 +152,7 @@ with_perl	= @with_perl@
 with_python	= @with_python@
 with_tcl	= @with_tcl@
 with_openssl	= @with_openssl@
+with_libxml	= @with_libxml@
 with_zlib	= @with_zlib@
 enable_shared	= @enable_shared@
 enable_rpath	= @enable_rpath@