Still another round of Perl-module installation tweaks.

Now, src/interfaces/perl5/Makefile.PL is pretty simple, and instead we
work a little harder in src/interfaces/Makefile.

src/interfaces/perl5/Makefile.PL.in → src/interfaces/perl5/Makefile.PL

 #-------------------------------------------------------
 #
-# $Id: Makefile.PL.in,v 1.1 1998/10/16 05:58:22 momjian Exp $
+# $Id: Makefile.PL,v 1.14 1998/10/18 02:36:48 tgl Exp $
 #
 # Copyright (c) 1997, 1998  Edmund Mergl
 #
@@ -14,19 +14,33 @@ my %opts;
 
 if (! $ENV{POSTGRES_HOME}) {
 
+    # Check that we actually are inside the Postgres source tree
+    if (! -d "../libpq") {
+	die
+"To install Pg separately from the Postgres distribution,
+you must set environment variable POSTGRES_HOME to point to
+where Postgres is installed (often /usr/local/pgsql).\n";
+    }
+
+    # Setup for build/test inside a Postgres source tree
+
+    # Perl may complain if path to libpq isn't absolute
     my $cwd = `pwd`;
     chop $cwd;
 
     %opts = (
         NAME         => 'Pg',
         VERSION_FROM => 'Pg.pm',
-        INC          => "-I$cwd/../libpq -I$cwd/../../include",
+        INC          => "-I../libpq -I../../include",
         OBJECT       => "Pg\$(OBJ_EXT)",
-        LIBS         => ["-L@prefix@/lib -L$cwd/../libpq -lpq"],
+        LIBS         => ["-L$cwd/../libpq -lpq"],
     );
 
 } else {
 
+    # Setup for final install of Pg using an already-installed libpq,
+    # or for standalone installation when Postgres already is installed.
+
     %opts = (
         NAME         => 'Pg',
         VERSION_FROM => 'Pg.pm',