On Windows "git clone url path/repo" does not create 'path' if it does
not exist. It fails with:

Fatal: could not create work tree dir 'path\repo'.: No such file or directory

this patch manually creates the subdir if it does not exist.
Review URL: http://codereview.chromium.org/7080063

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@87522 0039d316-1c4b-4281-b951-d872f2087c98