pgsql: WAL for GiST.

Log Message:
-----------
WAL for GiST. It work for online backup and so on, but on
recovery after crash (power loss etc) it may say that it can't restore
index and index should be reindexed.

Some refactoring code.

Modified Files:
--------------
pgsql/src/backend/access/gist:
Makefile (r1.12 -> r1.13)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/gist/Makefile.diff?r1=1.12&r2=1.13)
gist.c (r1.118 -> r1.119)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/gist/gist.c.diff?r1=1.118&r2=1.119)
gistget.c (r1.47 -> r1.48)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/gist/gistget.c.diff?r1=1.47&r2=1.48)
pgsql/src/backend/access/transam:
rmgr.c (r1.19 -> r1.20)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/transam/rmgr.c.diff?r1=1.19&r2=1.20)
pgsql/src/include/access:
gist_private.h (r1.2 -> r1.3)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/access/gist_private.h.diff?r1=1.2&r2=1.3)

Added Files:
-----------
pgsql/src/backend/access/gist:
gistutil.c (r1.1)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/gist/gistutil.c?rev=1.1&content-type=text/x-cvsweb-markup)
gistxlog.c (r1.1)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/gist/gistxlog.c?rev=1.1&content-type=text/x-cvsweb-markup)