pgsql: Upgrade to Autoconf 2.61: - Change configure.in to use Autoconf

Log Message:
-----------
Upgrade to Autoconf 2.61:
- Change configure.in to use Autoconf 2.61 and update generated files.
- Update build system and documentation to support now directory variables
offered by Autoconf 2.61.
- Replace usages of PGAC_CHECK_ALIGNOF by AC_CHECK_ALIGNOF, now available
in Autoconf 2.61.
- Drop our patched version of AC_C_INLINE, as Autoconf now has the change.

Modified Files:
--------------
pgsql:
configure (r1.579 -> r1.580)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/configure?r1=1.579&r2=1.580)
configure.in (r1.547 -> r1.548)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/configure.in?r1=1.547&r2=1.548)
pgsql/config:
c-compiler.m4 (r1.14 -> r1.15)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/config/c-compiler.m4?r1=1.14&r2=1.15)
programs.m4 (r1.21 -> r1.22)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/config/programs.m4?r1=1.21&r2=1.22)
pgsql/doc:
Makefile (r1.29 -> r1.30)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/Makefile?r1=1.29&r2=1.30)
pgsql/doc/src/sgml:
installation.sgml (r1.301 -> r1.302)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/installation.sgml?r1=1.301&r2=1.302)
pgsql/src:
Makefile.global.in (r1.240 -> r1.241)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/Makefile.global.in?r1=1.240&r2=1.241)
pgsql/src/include:
pg_config.h.in (r1.127 -> r1.128)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/pg_config.h.in?r1=1.127&r2=1.128)