Add support for perforce to help support Turbulence

[danmayer]

This would help with porting over Turbulence to use churn to power its graphs

https://github.com/chad/turbulence/tree/master/lib/turbulence/scm

[danmayer]

I worked on this but got stalled because I have never used perforce so getting a fake project setup for testing has been limiting... Some resources in progress below:

• http://www.perforce.com/downloads/Perforce-Software-Version-Management/complete_list/20-20#6
• http://www.endlesslycurious.com/2008/11/11/configuring-p4-command-line-client-on-mac-os-x/
• https://www.assembla.com/code/exampledan/perforce/repo/instructions?empty=true
• http://www.perforce.com/perforce/r10.1/manuals/p4v-gs/01_p4v-gs.html

I created a empty perforce repo on assembla so I should be able to try that out to move forward.