changing WORKSPACE maven_jar name mappings does not invalidate state

[johnynek]

After an error like #588 I had to do a bazel clean to fix the state.

Seems like a change to WORKSPACE should be detected, and if any of the names map to new jars the old external jars should be removed.

[johnynek]

I'm a bit worried that this bug could be more serious with this:

The fix for #337
8ca065c

I didn't see any tests that made sure that when a macro changes that we invalidate the workspace correctly.

/cc @damienmg

[damienmg]

Lukacs recently fix that I believe (this bug I mean), can you confirm?

The skylark dependency is added correctly (we share the code for the build file) but you are right we should add a test, see #672

[kchodorow]

Closing as this should have been fixed by recent changes, please comment if it's still and issue for you.