pgsql: Move the responsibility for calling StartupXLOG into

Log Message:
-----------
Move the responsibility for calling StartupXLOG into InitPostgres, for
those process types that go through InitPostgres; in particular, bootstrap
and standalone-backend cases.  This ensures that we have set up a PGPROC
and done some other basic initialization steps (corresponding to the
if (IsUnderPostmaster) block in AuxiliaryProcessMain) before we attempt to
run WAL recovery in a standalone backend.  As was discovered last September,
this is necessary for some corner-case code paths during WAL recovery,
particularly end-of-WAL cleanup.

Moving the bootstrap case here too is not necessary for correctness, but it
seems like a good idea since it reduces the number of distinct code paths.

Modified Files:
--------------
    pgsql/src/backend/bootstrap:
        bootstrap.c (r1.260 -> r1.261)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/bootstrap/bootstrap.c?r1=1.260&r2=1.261)
    pgsql/src/backend/tcop:
        postgres.c (r1.592 -> r1.593)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/tcop/postgres.c?r1=1.592&r2=1.593)
    pgsql/src/backend/utils/init:
        postinit.c (r1.208 -> r1.209)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/init/postinit.c?r1=1.208&r2=1.209)