polish the simplemerge command; add a test

actually port simplemerge to hg - use bdiff instead of patiencediff; this is a larger change, since bdiff works on 2 multi-line strings, while patiencediff works on 2 lists; - rename the main class from Merge3 to Merge3Text and add a Merge3 class that derives from Merge3Text. This new Merge3 class has the same interface from the original class, so that the tests still work; - Merge3 uses util.binary to detect binary data and raises util.Abort instead of a specific exception; - don't use the @decorator syntax, to keep python2.3 compatibility; - the test uses unittest, which likes to print how long it took to run. This obviously doesn't play too well with hg's test suite, so we override time.time to fool unittest; - one test has a different (but still valid) output because of the different diff algorithm used; - the TestCase class used by bzr has some extras to help debugging. test-merge3.py used 2 of them: - log method to log some data - assertEqualDiff method to ease viewing diffs of diffs We add a dummy log method and use regular assertEquals instead of assertEqualDiff. - make simplemerge executable and add "#!/usr/bin/env python" header

Import 3-way merge code from bzr merge3.py is imported as contrib/simplemerge test_merge3.py is imported as tests/test-simplemerge.py