message clarifications

The following messages from the postgres catalog either appear to be
internal errors that should be marked differently, or they are in my
estimation unintelligible to users and should be rephrased.


#: commands/async.c:1424
msgid "pg_notify queue is %.0f%% full"


#: storage/ipc/procarray.c:2224
msgid "record known xact %u latestObservedXid %u"


#: storage/ipc/procarray.c:2257
msgid "recording unobserved xid %u (latestObservedXid %u)"


#: storage/ipc/procarray.c:2379
msgid "too many KnownAssignedXids"


#: storage/ipc/standby.c:861
msgid ""
"snapshot of %u running transactions overflowed (lsn %X/%X oldest "
"xid %u next xid %u)"


#: storage/ipc/standby.c:868
msgid ""
"snapshot of %u running transaction ids (lsn %X/%X oldest xid %u "
"next xid %u)"


Help please.