Adds a job->cfr boolean to indicate "encode this with a constant frame rate" instead...

Adds a job->cfr boolean to indicate "encode this with a constant frame rate" instead of passing through the true frame durations from the source. Includes CLI implementation, which sets cfr to 1 if the user specifies a frame rate. Otherwise, it uses "same as source" frame rate.

git-svn-id: svn://localhost/HandBrake/trunk@1496 b64f7644-9d1e-0410-96f1-a4d463321fa5