This reverts commit 9117985b in favor of
a more general solution.

Thomas Munro

building contrib with USE_PGXS.  To make it work all the way, the
pg_regress script would need to be included in the installation tree.

for testing PLs and contrib_regression for testing contrib, instead of
overwriting the core system's regression database as formerly done.
Andrew Dunstan

some massaging by Peter Eisentraut.  This is basically a simple
generalization of the existing contrib makefiles.

$Header: -> $PostgreSQL Changes ...

the source tree.

outside the source tree.

(Not that it will actually work with 7.3, I fear.)

Eliminate the mysterious games that the Cygwin build plays with the linker
flag variables.  DLLLIBS is gone, use SHLIB_LINK like everyone else.
Detect cygipc in configure, after the linker flags are set up, otherwise
configure might not work at all.

Make sure everything is covered by make clean.

Fix the build of the new conversion procedure modules.

Add new DLLIMPORT markers where required.

Finally, the compiler complains if we use an explicit
-I/usr/local/include, so don't do that.  Curiously, -L/usr/local/lib is
still necessary.

under libdir, for a cleaner separation in the installation layout
and compatibility with binary packaging standards.  Point backend's
default search location there.  The contrib modules are also
installed in the said location, giving them the benefit of the
default search path as well.  No changes in user interface
nevertheless.

written a generic framework of rules that the contrib makefiles can
use instead of writing their own each time.  You only need to set a few
variables and off you go.