Remove .git suffix on destination directory if URL ends with it.

For example, the following:

    homesick clone git://github.com/technicalpickles/pickled-vim.git

should produce a castle directory of:

    $HOME/.homesick/repos/pickled-vim
Merge pull request #40 from fnichol/fix-clone-destination

Remove .git suffix on destination directory if URL ends with it.