Update ruby-pg to 0.16.0.

== v0.16.0 [2013-07-22] Michael Granger <ged@FaerieMUD.org>

Bugfixes:

- Avoid warnings about uninitialized instance variables.
- Use a more standard method of adding library and include directories.
  This fixes build on AIX (Github #7) and Solaris (#164).
- Cancel the running query, if a thread is about to be killed (e.g. by CTRL-C).
- Fix GVL issue with wait_for_notify/notifies and notice callbacks.
- Set proper encoding on the string returned by quote_ident, escape_literal
  and escape_identifier (#163).
- Use nil as PG::Error#result in case of a NULL-result from libpq (#166).
- Recalculate the timeout of conn#wait_for_notify and conn#block in case
  of socket events that require re-runs of select().

Documentation fixes:

- Fix non working example for PGresult#error_field.

Enhancements:

- Add unique exception classes for each PostgreSQL error type (#5).
- Return result of the block in conn#transaction instead of nil (#158).
- Allow 'rake compile' and 'rake gem' on non mercurial repos.
- Add support for PG_DIAG_*_NAME error fields of PostgreSQL-9.3 (#161).

(taca)