merge3 code from bazaar-ng

[Aneesh Kumar]

Hi,

I am not sure what the code is or how good it is. But may be one of
the developers can take a look . I found the below information at

http://sourcefrog.net/weblog/software/vc/bzr

"One outcome of the research side is modules to do the fundamental vc
algorithms of 3-way merge and weave in pure Python. A few people have
suggested that merge3 in particular might usefully be contributed back
into the Python standard library; after a bit more maturation I'll
look into that. These have practical use in allowing it to be
installed and run without any extra dependencies like GNU diff; this
is moderately important on windows."

-aneesh