Add "drush make" file for automatically installing glip

When using drush makefiles, this file will trigger automatic glip installation by way of drush recursive makefile parsing.
There are 2 patches in this issue:
-One for installing glip in sites/all/modules/git_deploy/glip
-Another for installing glip in sites/all/libraries. It also declares libraries module dependecy, thus triggering its download.
I did two, since it's not clear to me which location is correct and there are unresolved issues with 'libraries' location. Pick only one of them.

I temporary cloned git_deploy repo at https://bitbucket.org/amontero/git_deploy to test it without needing to wait for commit here.
Paste the following in test-git-deploy.make file:

core = 7.x
api = 2

projects[] = drupal

projects[git_deploy][type] = "module"
projects[git_deploy][download][type] = "git"
projects[git_deploy][download][url] = "git@bitbucket.org:amontero/git_deploy.git"
projects[git_deploy][download][branch] = "modules"

I use 'modules' branch here for testing, but you can also test against 'libraries' branch. Thus you can easily test both locations.
To run it, just type "drush make test-git-deploy.make". You will get a fresh Drupal+git_deploy with glip installed for free :)
When other glip version is required, just tweak the glip_deploy.make entries and drush make users will not need to install by hand.