Make PGLO-READ a generic function, with specializations on the v2 and
v3 protocols. The difference is necessary because the v2 protocol
reads large-object data in text, whereas the v3 protocol changed to
use a binary format.

darcs-hash:6639fd1b9dd10ca051ea03d7e2fbff94c0d917e2

Implement binary-mode transfers for large-object operations in the v3
protocol. The v2 protocol transfers arguments in binary mode, but the
v3 protocol requires the client to specify for each argument of a
FunctionCall whether it is encoded as binary or as text.

  - add possibility to send (unsigned-byte 8) arguments to function calls

  - add a method READ-OCTETS-FROM-PACKET that reads raw octets

  - make PG-IMPORT and PG-EXPORT use binary I/O

  - PGLO-READ reads data in binary

  - change the large-object tests to use binary I/O (fixes the pglo test)

darcs-hash:bda38e377fe3d2bf89d34065e942299e065fdd90

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