Add support for compacting DBusStrings to release wasted memory.

Add support for compacting DBusStrings to release wasted memory.

2007-09-19  Ryan Lortie  <desrt@desrt.ca>

        * dbus/dbus-string.[ch] (compact, _dbus_string_compact,
        _dbus_string_lock): new compact function to free up allocated memory
        that is no longer used.

        * dbus/dbus-message.c (load_message): call _dbus_string_compact on the
        message loader buffer.

        * dbus/dbus-transport-socket.c (do_reading, do_writing): call
        _dbus_string_compact on the incoming/outgoing "encoded" buffers.

        * dbus/dbus-string-util.c (_dbus_string_test): add a few tests for
        string compacting.