The previous implementation was fine to catch timeout of third-party
tools (like dot), but to good to catch timeout in Spot itself, because
Python will not deliver a SIGALRM while a native function (e.g. Spot's
translation) is running. So we fork() the Python process, with a
parent that does nothing but wait for the termination of the child or
for an alarm. On SIGALRM, the parent kills all children.
* wrap/python/ajax/spot.in: Adjust to fork.
* wrap/python/tests/alarm.py: New test file to test this
scenario in a more controled environment.
* wrap/python/tests/Makefile.am: Add it.
