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

Code cleanups.

darcs-hash:accdbe4ec375dd9630c452cea382a94d5886ed06

Integrate Peter Van Eynde's v3 protocol support:

   - create PGCON-V2 and PGCON-V3 classes
   - PG-CONNECT attempts to connect using v3 protocol, and falls back
     to v2 protocol for older backends; return a PGCON-V2 or PGCON-V3
     object
   - PG-EXEC and FN and PG-DISCONNECT are generic functions that
     dispatch on the connection type
   - protocol code split into v2-protocol.lisp and v3-protocol.lisp

TBD: cleaning up the notification & error reporting support, and
factorizing more code between the two protocol versions.

Also split code out into multiple files:

   - large-object support
   - metainformation about databases
   - parsing and type coercion support
   - utility functions and macros

darcs-hash:00b6e900f7b48953d959f95e55c26ecee52efb37