D150312 added a TODO:
TODO: consider renaming the field StartAtCycle and Cycles to
AcquireAtCycle and ReleaseAtCycle respectively, to stress the
fact that resource allocation is now represented as an interval,
relatively to the issue cycle of the instruction.
This patch implements that TODO. This naming clarifies how to use these
fields in the scheduler. In addition it was confusing that StartAtCycle was
singular but Cycles was plural. This renaming fixes this inconsistency.