Removed abbreviation of cd to Proj

This isn't because I don't like the idea of vim being able to handle a
"project" where it keeps NERDTree and VimShell and the :cd all at the
same place so much as just that it doesn't work that well since when
vimshell comes into the equation it will need to know what the current
window layout looks like to open itself in an appropriate place. Also,
even if I don't account for vimshell I still lose my ability to control
the current :cd independently of NERDTree which is nice. Maybe in the
future a plain ol' Proj command might work to this effect but for now
since I can't see my way through to getting it to work with vimshell
easily I'm thinking the best strategy is to not mess with the :cd in vim
too much after it's been set initially (i.e. one vim instance per
directory for the most part)