git-svn: extract reusable code into utility functions

git-svn: extract reusable code into utility functions

Extacted canonicalize_path() in the main package.

Created new Git::SVN::Util package with an md5sum() function.  A
new package was created so that Digest::MD5 did not have to be
loaded in the main package.  Replaced code in the SVN::Git::Editor
and SVN::Git::Fetcher packages with calls to md5sum().

Extracted the format_svn_date(), parse_git_date() and
set_local_timezone() functions within the Git::SVN::Log package.

Signed-off-by: David D. Kilzer <ddkilzer@kilzer.net>
Acked-by: Eric Wong <normalperson@yhbt.net>