Add overload of TestWatcher.skipped() that uses the external AssumptionViolationException.

This allows code using TestWatcher to handle assumption violation exceptions
without using deprecated classes.
Merge branch 'test-watcher-internal-assumption-violation' into test-watcher-delegation

Conflicts:
	src/test/java/org/junit/tests/experimental/rules/StopwatchTest.java
	src/test/java/org/junit/tests/experimental/rules/TestWatcherTest.java
runtime() should return a fixed time after the test ends
Merge pull request #928 from kcooney/test-watcher-internal-assumption-violation

Add overload of TestWatcher.skipped() that uses the external AssumptionViolationException
Merge branch 'master' into test-watcher-delegation