Adding the 'mk-repo' scripts.

The "mk-repo._*.sh" scripts are now created anytime my 'svn2git_*' tool
does an export.  The script contains the explicit 'git svn *' command
run to generate the new git repo.

Each of these "mk-repo._*.sh" scripts documents how the staging-area for
each subtree was created, in case that staging area needs to be
recreated.