Introduces a new test API, `includesModule`. The method returns whether
a particular module like "ajax" or "deprecated" is included in the current
jQuery build; it handles the slim build as well. The util was created so that
we don't treat presence of particular APIs to decide whether to run a test as
then if we accidentally remove an API, the tests would still not fail.
Closes gh-5071
Fixes gh-5069
Ref gh-5046
(partially cherry picked from commit fae5fee8b4)
Also, run `grunt npmcopy` to sync the "external" directory with dependencies
from package.json. For example, the Sinon library version didn't match.
Ref gh-4234
Closes gh-4297
