user debugger doesn't take signal handlers into account

[axeld]

When an unexpected_exception() occurs, the user debugger is invoked first, and only if it let the program running a signal is sent. If the application had a signal handler installed for the signal, it's not called. Tested with VLC 0.7.2 and hrev16543 - it crashes on startup (invalid opcode exception). If the user_debug_exception_occured() call is commented out, the signal handler is called correctly (but VLC hangs afterwards somewhere, but that should be another issue :-)).

[bonefish]

Fixed in revision 16556. user_debug_exception_occured() now checks whether a non-default handler is installed for the signal before installing a debugger.