This helps prevent behavior such as setting '--name .' so that the .gclient
file contains '.' as the name of the solution, and the .gclient file ends
up a sibling of the .git file, rather than a sibling of the git checkout's
containing directory.

R=iannucci@chromium.org, thestig@chromium.org

Review URL: https://codereview.chromium.org/1406053003

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@297343 0039d316-1c4b-4281-b951-d872f2087c98