Manual pages are already present in the PostgreSQL tarball, so we avoid
messing with timestamp: it depends on postgres.xml that, in turn,
depends on almost all SGML files, most notably, version.sgml.  And the
latter depends on the configure in the top-level directory, so when
we patch it, build system wants to regenerate manual pages.

--- doc/src/sgml/Makefile.orig	2011-09-13 23:42:58.508672251 +0400
+++ doc/src/sgml/Makefile	2011-09-13 23:43:01.676668807 +0400
@@ -75,8 +75,6 @@
 ## Man pages
 ##
 
-man distprep-man: man-stamp
-
 man-stamp: stylesheet-man.xsl postgres.xml
 	$(XSLTPROC) $(XSLTPROCFLAGS) $(XSLTPROC_MAN_FLAGS) $^
 	touch $@