fixed test/vimrc
fixes helptags and wildigore issue #390

- resolve introduced in 08e9894d2 resolves only bundle dir
- so '/doc/' dir doesn't loose its trailing slash
docs: explain directory argument to :Bundle

Add some documentation to explain the directory argument (optional second
argument) to the Bundle command.  Maybe fixes #295
Merge pull request #394 from lucc/issue-295

vundle.txt update: explain directory argument to :Bundle & fix Vundle path