Merge of lp:~jamesodhunt/upstart/upstream-udev+socket-bridges.

* Makefile.am: Added extra directory.
* New files:
  - extra/Makefile.am
  - extra/conf/upstart-socket-bridge.conf
  - extra/conf/upstart-udev-bridge.conf
  - extra/man/socket-event.7
  - extra/man/upstart-socket-bridge.8
  - extra/man/upstart-udev-bridge.8
  - extra/upstart-socket-bridge.c
  - extra/upstart-udev-bridge.c
* configure.ac:
  - Check for udev (for upstart-udev-bridge).
  - Add extra/Makefile to AC_CONFIG_FILES.
* dbus/com.ubuntu.Upstart.xml: Add EmitEventWithFile method.
* init/control.c:
  - control_emit_event(): Now a wrapper for control_emit_event_with_file.
  - control_emit_event_with_file(): New function that operates on an fd.
* init/control.h: Prototype for control_emit_event_with_file().
* init/event.c:
  - event_new(): Initialize event fd.
  - event_pending_handle_jobs(): Now calls event_operator_fds().
* init/event.c: Add fd to Event struct.
* init/event_operator.c: event_operator_fds(): New function.
* init/event_operator.h: Prototype for event_operator_fds().
* init/job.c: job_new(): Initialize fd members.
* init/job.h: Add fds and num_fds to Job struct.