git-isvn(1): Integrated Subversion for Git.

git-isvn is a threaded C frontend for Git that pulls from Subversion
much faster than git-svn.perl, and most importantly, isn't written in
Perl.

WORKS:
  - clone (on some repositories, if you're careful)

TODO:
  - fetch (resumed clone) / persisted revmap
  - dcommit
  - continue to flesh out docs.
git-isvn(1): Start porting from git to libgit2.

It builds! Ship it.