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, and if it doesn't
    deadlock)

TODO:
  - fix deadlock issue in fetch
  - actually checkout a HEAD at end of clone
  - branching (set commit 'parent' for branch copies)
  - fetch (resumed clone) / persisted revmap
  - dcommit
  - continue to flesh out docs.