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

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.