git-svn: allow `info' command to work offline
git-svn: allow `info' command to work offline

Cache the repository root whenever we connect to the repository.
This will allow us to notice URL changes if the user changes the
URL in .git/config, too.

If the repository is no longer accessible, or if `git svn info'
is the first and only command run; then '(offline)' will be
displayed for "Repository Root:" in the output.

Signed-off-by: Eric Wong <8c2951295f8292b0c03727bc4652981172298eae@yhbt.net>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git