Comment 4 for bug 699264

Here is a test program for signal handling
in multi-threaded environment.

The results for Fedora Core {4,8} are:
errors like segmentation fault are handled with
the same thread that generated them (naturally);
this means that signal handler may be reentered.
most importantly, blocking signals in one thread
does not block them for other threads, so additional
synchronisation is needed in case of emergency saves.