pg_notifies statement is eliminated, and callbacks defined by
pg_listen are instead invoked automatically from the Tcl idle loop
whenever a NOTIFY message is received.

I have done only cursory testing, so there may be problems still
lurking (particularly on non-Unix machines?).  But it seems to
work.

Patch is against today's cvs sources.  Note that this will not work
with the 6.3.2 release since it depends on the new libpq.

The diffs are a bit large so I've gzipped them.  A patch to update
libpgtcl.sgml is included too.

			regards, tom lane