If no errors exist, the status-line will inform users how to view the
Changelog after BundleUpdate! is completed.

Instead of creating a vundle_update tag to compare changes between update
and HEAD we now use the output from `git pull` to get initial/updated shas.

Distinction between `new` and `updated` simplifies the process
of adding a bundle to the updated_bundle list.

Keeps track of the current commit with a vundle_update tag before
perfoming an update and adds all commits pulled in the update to a
Changelog accessible via pressing 'u' after BundleInstall! completes.

- having it as a function makes it slower

- "transcient bundle" - a bundle installed with :BundleInstall or interactively
  without being declared in .vimrc

- treat them the as if they were configured
- so everything works the same

- ie before this change helptags weren't generated automatically
  with `BundleInstall bundle` or with interactive mode

- it changes the way `:BundleClean` works, since it removes directories
  that aren't bundles
- FIX: `:source .vimrc` to let `:BundleClean` remove transcient bundles

- closes #99

- closes #104

- closes #110

Also save/restore input so potential mappings aren't broken.

- use `redraw` instead `redraw!`
- closes #90

- to avoid accidental removal

- show installation destination

- batch process just iterates through the lines and calls specified
action
- individual actions give visual feedback aswell
- allow Helptags command as a part of installation process

- log is global array so log can be viewed any time
- log gets written to a defined location ~/.vim-vundle/vundle.log
- TODO: write log changes as they happen

BundleInstall sources the current vimrc in order to reload all Bundles
in order to consider new Bundles that might have been added by the user
directly on their vimrc file. This, however, should not be Vundle's
responsibility, changes in vimrc should not be applied unless it is
re-sourced explicitly by the user.

This makes Vundle use the known list of Bundles for installation.

- but don't like it

- TODO: refactor: extract common code

Installer buffer is marked as modified after each installation. Mark it
as nomodified so that no warnings are shown when the buffer is closed.

- otherwise confusing with updated