pgsql: Remove the recently added USE_SEGMENTED_FILES option, and indeed

Log Message:
-----------
Remove the recently added USE_SEGMENTED_FILES option, and indeed remove all
support for a nonsegmented mode from md.c. Per recent discussions, there
doesn't seem to be much value in a "never segment" option as opposed to
segmenting with a suitably large segment size. So instead provide a
configure-time switch to set the desired segment size in units of gigabytes.
While at it, expose a configure switch for BLCKSZ as well.

Zdenek Kotala

Modified Files:
--------------
pgsql:
configure (r1.591 -> r1.592)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/configure?r1=1.591&r2=1.592)
configure.in (r1.557 -> r1.558)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/configure.in?r1=1.557&r2=1.558)
pgsql/doc/src/sgml:
installation.sgml (r1.307 -> r1.308)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/installation.sgml?r1=1.307&r2=1.308)
storage.sgml (r1.22 -> r1.23)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/storage.sgml?r1=1.22&r2=1.23)
pgsql/src/backend/storage/file:
buffile.c (r1.30 -> r1.31)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/file/buffile.c?r1=1.30&r2=1.31)
pgsql/src/backend/storage/smgr:
md.c (r1.137 -> r1.138)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/smgr/md.c?r1=1.137&r2=1.138)
pgsql/src/include:
pg_config.h.in (r1.130 -> r1.131)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/pg_config.h.in?r1=1.130&r2=1.131)
pg_config_manual.h (r1.31 -> r1.32)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/pg_config_manual.h?r1=1.31&r2=1.32)