Add GDS Verify module changes

GDS Verify(IDA) project use a fork of this graphite module. It seems like a good idea to incorporate changes in to this module, with the view the Verify project dropping the fork and using only this module.

The GDS Verify additional changes are:
 - Ability to specify the user used to run the processes
 - Install from Debian package
 - Some carbon cache options
> @samjsharpe I basically had to do a merge between two directories and as a result lost commit history from the the IDA module :disappointed:, since the IDA module is not a separate repo but a directory within a repo. So commit 254549e is pretty much a big bang commit with all the differences between IDA and this repo. 

You can keep history by using [subtree merging](http://git-scm.com/book/en/v1/Git-Tools-Subtree-Merging) to merge this repo with a subtree (aka subdirectory) of the IDA repo.  You might be able to do something with filter-branch as well. I can help with this on monday if you want.