[PATCH-revised] common test code for timed bail out

The attached patch addresses the following Perl TODO:

=head2 common test code for timed bail out

Write portable self destruct code for tests to stop them burning CPU in
infinite loops. This needs to avoid using alarm, as some of the tests are
testing alarm/sleep or timers.

This revision incorportates the latest comments.
Further discussion encouraged.

• [PATCH] common test code for timed bail out by Jerry D. Hedden
• Re: [PATCH] common test code for timed bail out by Nicholas Clark
• Re: [PATCH] common test code for timed bail out by Jerry D. Hedden
• Re: [PATCH] common test code for timed bail out by Jerry D. Hedden
• RE: [PATCH] common test code for timed bail out by Jan Dubois
• [PATCH-revised] common test code for timed bail out by Jerry D. Hedden
• Re: [PATCH-revised] common test code for timed bail out by Ben Morrow
• Re: [PATCH] common test code for timed bail out by Nicholas Clark
• Re: [PATCH] common test code for timed bail out by Jerry D. Hedden
• RE: [PATCH] common test code for timed bail out by Steve Hay
• Re: [PATCH] common test code for timed bail out by Jerry D. Hedden
• RE: [PATCH] common test code for timed bail out by Jan Dubois