Subversion support

[Thomas Braun]

Hi,

I started some time ago to get the subversion stuff compiled in order
to get "git svn" working.

This turned out to be really hairy, in the conclusion "git svn help"
always crashed.

I'll will not put any more work into that, as I don't really use svn
anymore.

If someone wants to get a start, my branch [1] might spare some hours.

Thomas

[1]: https://github.com/t-b/sdk-packages/tree/msys-subversion-and-deps