git-svn: Add --localtime option to "fetch"

git-svn: Add --localtime option to "fetch"

By default git-svn stores timestamps of fetched commits in
Subversion's UTC format.  Passing --localtime to fetch will convert
them to the timezone of the server on which git-svn is run.

This makes the timestamps of a resulting "git log" agree with what
"svn log" shows for the same repository.

Signed-off-by: Pete Harlan <pgit@pcharlan.com>
Acked-by: Eric Wong <normalperson@yhbt.net>