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
Why has this value changed? As my comment above, this is also not explained in the commit where it changes (254549ea), if that could be rebased to include explanation and to separate out the different things that are going on that would also be useful.