Issue #1095 - MAV_CMD_DO_CHANGE_SPEED

Here is a my proposition to manage the MAV_CMD_DO_CHANGE_SPEED command_long. (Issue #1095)

There are quite a lot of files because I added a unit test environnement to check my modification. It will be now pretty easier to add tests for the GCS_Mavlink.pde file.

By the way the *real* modification is short and located in GCS_Mavlink.pde.

I tried to respect all of your coding conventions, if anything is missing, please tell me.

Valentin