[RFC] internal patch implementation

[Chris Mason]

Hello everyone,

I've started integrating my mpatch tool into hg.  The first step is
using the code to apply context/unified/git diffs directly in mercurial,
without calling gnu patch.

Performance looks good so far, applying the entire mm tree is 10s faster
overall (1m6s vs 56s).  The entire difference is in system time.

You can take a look and/or try it out here:

http://oss.oracle.com/mercurial/mason/hg-mpatch

Step two is to integrate the reject resolving features into hg qpush,
but that is only interesting after the code to apply patches is well
tested and everyone is happy.

make tests reports some small differences in output, but these look
harmless so far.

-chris