Integrate mods from WEB-CAT

[whart222]

• Signal protection support so that test cases that fail
  with program crashes (particularly segfaults) don't terminate
  a test run, and are instead treated as test case failures,
  allowing the remaining tests in a suite to run.
• Support for customizable error messages when tests fail
  due to signals, instead of failed assertions.
• Support for test listeners, so that multiple independent
  listeners can receive callbacks on test results, allowing
  alternative result formatters to be targetted to different
  output destinations.
• Support for testing main programs by redirecting stdio.
• Support for memory management tracking, spotting memory
  leaks, and detecting all kinds of pointer manipulation
  errors.

See http://web-cat.cvs.sourceforge.net/viewvc/web-cat/CxxTest%2BDereferee%20Master/CxxTest/