Fix to timezone handling when parsing timestamps (timezone offset can
be negative).

From Katsuya Tomioka.

darcs-hash:656ed17ea7f0d6b56554558f2a5e7f67e60d032d

Add support for the SQL NUMERIC type, thanks to Risto Sakari Laakso.
Was previously being parsed as an integer, but is in fact a fix-precision
floating-point number.

darcs-hash:23c7961c351a7e66d96ad0caccba1d1e7a16f501

layout of documentation

darcs-hash:ab4b9a109a6938f748f5e764c16f07d7fcbb370c

More factorization of lowlevel functions between v2 and v3 protocols.

darcs-hash:aef9e7feac79e0d6b749d3ff999a62e1f50c4d69

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