Add full variant to the approximate timeout functiont

Add full variant to the approximate timeout functiont

The g_timeout_add_seconds() API lacks a _full() counterpart, allowing the
setting of a destroy notification function to be invoked when the timeout
source is removed.

This patch adds g_timeout_add_seconds_full() to the public API and
reimplements g_timeout_add_seconds() as a call to g_timeout_add_seconds_full().

svn path=/trunk/; revision=5575