This commit introduces `rev-parse HEAD` in order to parse the commits at
which HEAD points before and after `git pull`. If the commits are the
same, the bundle is considered 'up-to-date'. If the commits are different,
then the HEAD was fast-forwarded and the bundle is considered 'updated'.

This approach is more reliable than parsing the output of the `git` command
as it can differ between OSes and locales.

Tested on Ubuntu 11.10. The control characters at the end of the output of
`git rev-parse` are stripped away using '[:cntrl:]', assuming cross-platform.

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.

If the Bundle is hosted on GitHub include link to compare the commit range
visually on GitHub.

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.

- also work in batches

- having it as a function makes it slower

- as `http` one just redirects to `https` on GitHub

- use `let g:vundle_default_git_proto = 'git'` to set default protocol
to build URIs to clone from

- "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 #64

- closes #104

- closes #110

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

Prevents the user from having to type a space before the search term.

- closes #80

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

- to avoid accidental removal

- so it better reflects the content

- do not clutter up ~/

- not sure if there's a need for log file in predefined location
- installer is verbose enough to signal errors

- to avod error when deleting nonexisting buffer

- 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

- merge with view()
- no need for having both

- 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.