[plt-dev] Transferring "usr" data from svn to git

My main question is: once I have something in a git repository, can I
copy a subtree of one git repository into another, and keep the
history of that subtree?

If so, then I can reproduce my svn data in git any way I like now.  If
at any time later I decide I don't like the way I've split it up, I
can split things further or join things back together, preserving
history, by copying between repositories.

If not, then I have to be careful how I split things up now because I
won't be able to change repository structure later without losing some
of the history data.

I asked something like this on IRC, but I don't know that I spelled
the question out well enough, so I might as well get this settled "for
real" this time.

Carl Eastlund