Fix VPATH builds of the replication parser from git for some !gcc compilers.

Some compilers don't automatically search the current directory for
included files. 9cc2c182 fixed that for builds from tarballs by
adding an include to the source directory. But that doesn't work when
the scanner is generated in the VPATH directory. Use the same search
path as the other parsers in the tree.

One compiler that definitely was affected is solaris' sun cc.

Backpatch to 9.1 which introduced using an actual parser for
replication commands.

src/backend/replication/Makefile

@@ -12,7 +12,7 @@ subdir = src/backend/replication
 top_builddir = ../../..
 include $(top_builddir)/src/Makefile.global
 
-override CPPFLAGS := -I$(srcdir) $(CPPFLAGS)
+override CPPFLAGS := -I. -I$(srcdir) $(CPPFLAGS)
 
 OBJS = walsender.o walreceiverfuncs.o walreceiver.o basebackup.o \
 	repl_gram.o slot.o slotfuncs.o syncrep.o