pgsql: Extend yesterday's patch making BLCKSZ and RELSEG_SIZE

Log Message:
-----------
Extend yesterday's patch making BLCKSZ and RELSEG_SIZE configurable to also
let XLOG_BLCKSZ and XLOG_SEG_SIZE be set via configure. Per a proposal by
Mark Wong, though I thought it better to call the switches after "wal" rather
than "xlog".

Modified Files:
--------------
pgsql:
configure (r1.592 -> r1.593)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/configure?r1=1.592&r2=1.593)
configure.in (r1.558 -> r1.559)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/configure.in?r1=1.558&r2=1.559)
pgsql/doc/src/sgml:
installation.sgml (r1.308 -> r1.309)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/installation.sgml?r1=1.308&r2=1.309)
wal.sgml (r1.52 -> r1.53)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/wal.sgml?r1=1.52&r2=1.53)
pgsql/src/include:
pg_config.h.in (r1.131 -> r1.132)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/pg_config.h.in?r1=1.131&r2=1.132)
pg_config_manual.h (r1.32 -> r1.33)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/pg_config_manual.h?r1=1.32&r2=1.33)