BUG #1766: contrib/ modules can't install with --without-docdir

The following bug has been logged online:

Bug reference: 1766
Logged by: ISHIDA Akio
Email address: iakio(at)mono-space(dot)net
PostgreSQL version: 8.0.3
Operating system: Linux
Description: contrib/ modules can't install with --without-docdir
Details:

$ ./configure --without-docdir
..
$ cd contrib/pgstattuple/
$ make install
mkdir -p -- /contrib
mkdir: cannot create directory `/contrib': Permission denied
make: *** [installdirs] Error 1

--- src/makefiles/pgxs.mk.org 2004-10-11 01:13:03.000000000 +0900
+++ src/makefiles/pgxs.mk 2005-07-14 09:54:24.000000000 +0900
@@ -100,10 +100,12 @@
done
endif # MODULES
ifdef DOCS
+ifdef docdir
@for file in $(addprefix $(srcdir)/, $(DOCS)); do \
echo "$(INSTALL_DATA) $$file $(DESTDIR)$(docdir)/contrib"; \
$(INSTALL_DATA) $$file $(DESTDIR)$(docdir)/contrib; \
done
+endif # docdir
endif # DOCS
ifdef PROGRAM
$(INSTALL_PROGRAM) $(PROGRAM)$(X) $(DESTDIR)$(bindir)
@@ -133,8 +135,10 @@
$(mkinstalldirs) $(DESTDIR)$(pkglibdir)
endif
ifdef DOCS
+ifdef docdir
$(mkinstalldirs) $(DESTDIR)$(docdir)/contrib
-endif
+endif # docdir
+endif # DOCS
ifneq (,$(PROGRAM)$(SCRIPTS)$(SCRIPTS_built))
$(mkinstalldirs) $(DESTDIR)$(bindir)
endif