Blocked revisions 88467 via svnmerge

........
  r88467 | brett.cannon | 2011-02-21 11:29:56 -0800 (Mon, 21 Feb 2011) | 11 lines

  Issue python#10990: Prevent tests from clobbering a set trace function.

  Many tests simply didn't care if they unset a pre-existing trace function. This
  made test coverage impossible. This patch fixes various tests to put back any
  pre-existing trace function. It also introduces test.support.no_tracing as a
  decorator which will temporarily unset the trace function for tests which
  simply fail otherwise.

  Thanks to Kristian Vlaardingerbroek for helping to find the cause of various
  trace function unsets.
........