Support for DESTDIR make variable. This is used as in `make install

DESTDIR=/else/where' and prepends the value of DESTDIR to the full
installation paths (e.g., /else/where/usr/local/pgsql/bin). This allows
users to install the package into a location different from the one that
was configured and hard-coded into various scripts, e.g., for creating
binary packages.

DESTDIR is in many cases preferrable over `make install
prefix=/else/where' because

a) `prefix' affects the path that is hard-coded into the files, which can
lead to a `make install prefix=xxx' (as done by the regression test
driver) corrupting the files in the source tree with wrong paths.

b) it doesn't work at all if a directory was overridden to not depend on
`prefix', e.g., --sysconfdir=/etc.

(Updating the regression test driver to use DESTDIR is a separate
undertaking.)

See also autoconf@gnu.org, From: Akim Demaille <akim@epita.fr>, Date: 08
Sep 2000 12:48:59 +0200, Message-ID:
<mv4em2vb1lw.fsf@nostromo.lrde.epita.fr>, Subject: Re: HTML format
documentation.

src/pl/plperl/GNUmakefile

@@ -1,10 +1,10 @@
-# $Header: /cvsroot/pgsql/src/pl/plperl/GNUmakefile,v 1.3 2000/08/31 16:12:13 petere Exp $
+# $Header: /cvsroot/pgsql/src/pl/plperl/GNUmakefile,v 1.4 2000/09/17 13:02:51 petere Exp $
 
 subdir = src/pl/plperl
 top_builddir = ../../..
 include $(top_builddir)/src/Makefile.global
 
-plperl_installdir = $(libdir)
+plperl_installdir = $(DESTDIR)$(libdir)
 
 
 all: Makefile
@@ -16,13 +16,13 @@ Makefile: Makefile.PL
 	  $(PERL) $< POLLUTE=1
 
 install: all installdirs
-	$(MAKE) -f $< install
+	$(MAKE) -f Makefile install
 
 installdirs:
-	$(mkinstalldirs) $(plperl_installdir)
+	$(mkinstalldirs) $(DESTDIR)$(plperl_installdir)
 
 uninstall:
-	rm -f $(libdir)/plperl$(DLSUFFIX)
+	rm -f $(DESTDIR)$(libdir)/plperl$(DLSUFFIX)
 
 clean distclean maintainer-clean:
 	-[ -f Makefile ] && $(MAKE) -f Makefile clean