pgsql: Implement a few changes to how shared libraries and dynamically

Log Message:
-----------
Implement a few changes to how shared libraries and dynamically loadable
modules are built. Foremost, it creates a solid distinction between these two
types of targets based on what had already been implemented and duplicated in
ad hoc ways before. Specifically,

- Dynamically loadable modules no longer get a soname. The numbers previously
set in the makefiles were dummy numbers anyway, and the presence of a soname
upset a few packaging tools, so it is nicer not to have one.

- The cumbersome detour taken on installation (build a libfoo.so.0.0.0 and
then override the rule to install foo.so instead) is removed.

- Lots of duplicated code simplified.

Modified Files:
--------------
pgsql/src:
Makefile.shlib (r1.113 -> r1.114)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/Makefile.shlib?r1=1.113&r2=1.114)
pgsql/src/backend/snowball:
Makefile (r1.5 -> r1.6)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/snowball/Makefile?r1=1.5&r2=1.6)
pgsql/src/backend/utils/mb/conversion_procs:
proc.mk (r1.8 -> r1.9)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/mb/conversion_procs/proc.mk?r1=1.8&r2=1.9)
pgsql/src/interfaces/ecpg/compatlib:
Makefile (r1.39 -> r1.40)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/compatlib/Makefile?r1=1.39&r2=1.40)
pgsql/src/interfaces/ecpg/ecpglib:
Makefile (r1.58 -> r1.59)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/ecpglib/Makefile?r1=1.58&r2=1.59)
pgsql/src/interfaces/ecpg/pgtypeslib:
Makefile (r1.41 -> r1.42)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/pgtypeslib/Makefile?r1=1.41&r2=1.42)
pgsql/src/interfaces/libpq:
Makefile (r1.164 -> r1.165)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/libpq/Makefile?r1=1.164&r2=1.165)
pgsql/src/makefiles:
pgxs.mk (r1.11 -> r1.12)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/makefiles/pgxs.mk?r1=1.11&r2=1.12)
pgsql/src/pl/plperl:
GNUmakefile (r1.33 -> r1.34)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plperl/GNUmakefile?r1=1.33&r2=1.34)
pgsql/src/pl/plpgsql/src:
Makefile (r1.31 -> r1.32)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpgsql/src/Makefile?r1=1.31&r2=1.32)
pgsql/src/pl/plpython:
Makefile (r1.28 -> r1.29)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpython/Makefile?r1=1.28&r2=1.29)
pgsql/src/pl/tcl:
Makefile (r1.50 -> r1.51)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/tcl/Makefile?r1=1.50&r2=1.51)
pgsql/src/test/regress:
GNUmakefile (r1.72 -> r1.73)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/GNUmakefile?r1=1.72&r2=1.73)
pgsql/src/tutorial:
Makefile (r1.20 -> r1.21)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/tutorial/Makefile?r1=1.20&r2=1.21)