pgsql: Reduce size of critical section and remove call of user-defined

Log Message:
-----------
Reduce size of critical section and remove call of user-defined functions in
insertion and deletion, modify gistSplit() to do not use buffers.

 TODO: gistvacuumcleanup and XLOG

Modified Files:
--------------
    pgsql/src/backend/access/gist:
        gist.c (r1.132 -> r1.133)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/gist/gist.c.diff?r1=1.132&r2=1.133)
        gistutil.c (r1.10 -> r1.11)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/gist/gistutil.c.diff?r1=1.10&r2=1.11)
        gistvacuum.c (r1.19 -> r1.20)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/gist/gistvacuum.c.diff?r1=1.19&r2=1.20)
        gistxlog.c (r1.15 -> r1.16)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/gist/gistxlog.c.diff?r1=1.15&r2=1.16)
    pgsql/src/include/access:
        gist_private.h (r1.12 -> r1.13)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/access/gist_private.h.diff?r1=1.12&r2=1.13)