pgsql: More cleanups for the recent large object permissions patch.

Log Message:
-----------
More cleanups for the recent large object permissions patch.

Rewrite or adjust various comments for clarity.  Remove one bogus comment that
doesn't reflect what the code actually does.  Improve the description of the
lo_compat_privileges option.

Modified Files:
--------------
    pgsql/src/backend/catalog:
        aclchk.c (r1.157 -> r1.158)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/catalog/aclchk.c?r1=1.157&r2=1.158)
        pg_largeobject.c (r1.34 -> r1.35)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/catalog/pg_largeobject.c?r1=1.34&r2=1.35)
    pgsql/src/backend/commands:
        comment.c (r1.109 -> r1.110)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/comment.c?r1=1.109&r2=1.110)
    pgsql/src/backend/utils/adt:
        acl.c (r1.152 -> r1.153)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/acl.c?r1=1.152&r2=1.153)
    pgsql/src/backend/utils/misc:
        guc.c (r1.528 -> r1.529)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/guc.c?r1=1.528&r2=1.529)