Re: Correct handling of blank/commented lines in PSQL interactive-mode history

After some further hackery, here's a set of patches that I think
might be acceptable. They're actually fairly independent, although
they touch different aspects of the same behavior.

0001 gets rid of psqlscan.l's habit of suppressing dash-dash comments,
but only once we have collected some non-whitespace query input.
The upshot of this is that dash-dash comments will get sent to the
server as long as they are within the query proper, that is after the
first non-whitespace token and before the ending semicolon. Comments
that are between queries are still suppressed, because not doing that
seems to result in far too much behavioral change. As it stands,
though, there are just a few regression test result changes.

0002 is a simplified version of Greg's patch. I think we only need
to look at the state of the query_buf to see if any input has been
collected in order to determine if we are within or between queries.
I'd originally thought this'd need to be a lot more complicated,
but as long as psqlscan.l continues to drop pre-query comments,
this seems to be enough.

0003 is the same patch I posted before to adjust M-# behavior.

regards, tom lane