Your marking of the 'coverage' target as a phony got me considering which targets should actually be marked as phony targets.  According to this [stack overflow question][stack], it's probably best for us to mark all of our flags as phony because none of them result in a file being created with the same name.  I've updated the code in the change request accordingly.

[stack]: http://stackoverflow.com/questions/2145590/what-is-the-purpose-of-phony-in-a-makefile