Add an ABORT keyword argument to PG-DISCONNECT (from Robert J.
Macomber <pgsql@rojoma.com>), as per CL:CLOSE.

  "I've run into a problem with pg-disconnect if something abnormal
   happens to the database connection -- if the database goes away for a
   restart while pg has a connection open, for example.  When this
   happens, pg-disconnect fails, and the socket file descriptor is left
   open (presumably for a finalizer to clean up), also raising a new
   error from the unwind-protect in with-pg-connection.  To guard against
   the possibility, I've added an :abort parameter to pg-disconnect, like
   cl:close has, and made with-pg-connection call it with :abort t if the
   body exits abnormally, in the same way that with-open-file operates.
   When :abort is true, the modified pg-disconnect closes the database
   connection ungracefully, including making the close call abort
   (otherwise, sbcl at keast tries to flush the stream, raising another
   error if the database isn't there anymore)."

darcs-hash:aad628cf0093846dca55fe4f8fa47b0db89249c2