Fix phpunit @covers tags for coverage output.

Unfortunately, there are some bogus @covers tags in the test suite that prevent neat things like `phpunit --coverage-html` from working. With this fix, we can view the testing coverage, and have a better view on what to fix in the future.
(Sorry, a lot of these are mine from a recent push! ack.) :(
See https://phpunit.de/manual/3.7/en/appendixes.annotations.html#appendixes.annotations.covers for details on the expected format. (most notably, the double-colon for functions defined outside of a class)