Update ruby-pg to 0.15.0.

== v0.15.0 [2013-03-03] Michael Granger <ged@FaerieMUD.org>

Bugfixes:

- Fix segfault in PG::Result#field_values when called with non String value.
- Fix encoding of messages delivered by notice callbacks.
- Fix text encoding for Connection#wait_for_notify and Connection#notifies.
- Fix 'Bad file descriptor' problems under Windows: wrong behaviour of
  #wait_for_notify() and timeout handling of #block on Ruby 1.9.

Documentation fixes:

- conn#socket() can not be used with IO.for_fd() on Windows.

Enhancements:

- Tested under Ruby 2.0.0p0.
- Add single row mode of PostgreSQL 9.2.
- Set fallback_application_name to programm name $0. Thanks to Will Leinweber
  for the patch.
- Release Ruby's GVL while calls to blocking libpq functions to allow better
  concurrency in threaded applications.
- Refactor different variants of waiting for the connection socket.
- Make use of rb_thread_fd_select() on Ruby 1.9 and avoid deprecated
  rb_thread_select().
- Add an example of how to insert array data using a prepared statement (#145).
- Add continous integration tests on travis-ci.org.
- Add PG::Result#each_row for iterative over result sets by row. Thanks to
  Aaron Patterson for the patch.
- Add a PG::Connection#socket_io method for fetching a (non-autoclosing) IO
  object for the connection's socket.

Specs:

- Fix various specs to run on older PostgreSQL and Ruby versions.
- Avoid fork() in specs to allow usage on Windows and JRuby.

(taca)