reinstall nerdtree from pathogen (as git submodule)
Fix gvimrc colors, finally

Turns out setting macvim_skip_colorscheme=1 is what I wanted.  All the color
scheming I did was overridden by the system gvimrc which set a shitty color
scheme and broke anything I didn't explicitly define.

Also, set the guifg colors to match what I get from the color picker from
iterm.  They're subtly different than the "ctermfg" type colors because I use a
special iterm theme that overrides them to a different color set.

And finally, drop gvimrc once and for all, now that I solved the colorscheme
issue.