sofia-sip/su_wait.h: added su_timer_deferrable(), su_task_wakeup(), su_root_set_max_defer(), su_root_get_max_defer() and su_task_deferrable().

Added implementation to different main-loop implementations in
libsofia-sip-ua/su.

Fixed su_task_is_running().

In libsofia-sip-ua/su, added tests for deferred timers.

In libsofia-sip-ua-glib/su-glib/su_source.c, added su_source_wakeup() and
su_source_is_running(). Using su_base_port_send() instead of
su_source_send(). Using su_base_port_deferable() and
su_base_port_max_defer(), too.

Re-recorded 20070723202419-65a35-c4025757e65c161384f6c38020defbe7d37c2890

darcs-hash:20090128180606-db55f-c0c7fe26e283746d13358bcb7870e0099531812c.gz