Vim: don't re-generate helptags on startup

Saves about 100ms per startup. Note that this means updating our bundle
becomes a two step process now:

  git submodule foreach git pull
  vim -c "call pathogen#helptags()"

Signed-off-by: Greg Hurrell <greg@hurrell.net>
Vim: update bundle

This done using:

  git submodule foreach git pull --recurse-submodules
  vim -c "call pathogen#helptags() | quit"

This originally included a YouCompleteMe update, but HEAD of master
there is currently broken for me, so I backed that out. For reference,
the update procedure there was:

  cd .vim/bundle/YouCompleteMe
  git submodule update --init --recursive
  ./install.sh

This is now complicated enough that I am going to make a bundle update
script. No, I am not going to reinvent Vundle. Nor am I going to install
Vundle. Or NeoBundle. Or VAM. I want something lean and minimal.

Signed-off-by: Greg Hurrell <greg@hurrell.net>
Vim: add update-bundle.sh script

An 11-line shell script. A little bit of automation without going
overboard.

Signed-off-by: Greg Hurrell <greg@hurrell.net>