pgsql: Redesign the patch for allocation of shmem space and LWLocks for

Log Message:
-----------
Redesign the patch for allocation of shmem space and LWLocks for add-on
modules; the first try was not usable in EXEC_BACKEND builds (e.g.,
Windows).  Instead, just provide some entry points to increase the
allocation requests during postmaster start, and provide a dedicated
LWLock that can be used to synchronize allocation operations performed
by backends.  Per discussion with Marc Munro.

Modified Files:
--------------
    pgsql/src/backend/storage/ipc:
        ipci.c (r1.88 -> r1.89)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/ipc/ipci.c.diff?r1=1.88&r2=1.89)
        shmem.c (r1.97 -> r1.98)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/ipc/shmem.c.diff?r1=1.97&r2=1.98)
    pgsql/src/backend/storage/lmgr:
        lwlock.c (r1.46 -> r1.47)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/lmgr/lwlock.c.diff?r1=1.46&r2=1.47)
    pgsql/src/include/storage:
        lwlock.h (r1.31 -> r1.32)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/storage/lwlock.h.diff?r1=1.31&r2=1.32)
        pg_shmem.h (r1.20 -> r1.21)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/storage/pg_shmem.h.diff?r1=1.20&r2=1.21)
        shmem.h (r1.48 -> r1.49)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/storage/shmem.h.diff?r1=1.48&r2=1.49)