Big disconnect_and_exit cleanup in pg_basebackup

Hi,

the previously sent "factor out pg_malloc and friends" patch
may call exit() in case of OOM during allocation and as a consequence,
PQfinish() won't get called, leaving an "unexpected EOF from client"
in the log.

Let's close this annoyance in pg_basebackup. The attached patch does
the following:

- adds a PQfinish() (actually PQfinishSafe()) call that was just posted
   in another thread
- replace all PQfinish() and PQclear() with their *Safe counterpart so
   a normal execution won't result in a crash because of calling PQfinish()
   on a stale pointer
- kill the disconnect_and_exit() macro, replace it with plain exit(),
   the atexit callback does the disconnect anyway.

Best regards,
Zoltán Böszörményi

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Zoltán Böszörményi
Cybertec Schönig & Schönig GmbH
Gröhrmühlgasse 26
A-2700 Wiener Neustadt, Austria
Web: http://www.postgresql-support.de
      http://www.postgresql.at/