It is better to put the server includes before the general includes, because in
Debian server version and libpq version might be different.

--- a/Makefile.global.in
+++ b/Makefile.global.in
@@ -83,7 +83,7 @@ PERL=			@PERL@
 SED=			@SED@
 subdir=$(slony_subdir)
 
-override CPPFLAGS := -I${pgincludedir} -I${pgincludeserverdir} $(CPPFLAGS)
+override CPPFLAGS := -I${pgincludeserverdir} -I${pgincludedir} $(CPPFLAGS)
 LDFLAGS =   -L${pglibdir} -L${pgpkglibdir} -lpq @NLSLIB@
 
 ifeq ($(GCC), yes)
--- a/configure
+++ b/configure
@@ -5234,7 +5234,7 @@ else
     " "$LINENO" 5
 fi
 
-CPPFLAGS="$TEMP_CPPFLAGS -I$PG_INCLUDEDIR -I$PG_INCLUDESERVERDIR"
+CPPFLAGS="$TEMP_CPPFLAGS -I$PG_INCLUDESERVERDIR -I$PG_INCLUDEDIR"
 
 
 case "${host_os}" in