Fix regexp pattern searching git-dir (via #4)

1. '/.git' is unnecessary under submodule directory.

    ex)
    **Parent repository**: `C:\home\dotfiles`
    **Submodule repository**: `C:\home\dotfiles\.git\modules\dotfiles\.vim\bundle\restart.vim\COMMIT_EDITMSG`
    **Submodule path**: `C:\home\dotfiles\dotfiles\.vim\bundle\restart.vim`

2. Support 'noshellslash'.