In two of the tests there were unlink() calls at the end of an
asynchronously executed function. These calls would sometimes end
up executing only after the test has finished and after cleanup,
leading to them erroring out due to target files no longer around.

These failures would cause exceptions reported in other, unrelated
tests. Since the tests containing them work just fine without the
unlink calls (as is evident by the fact that tests passed even if
they executed after finishing the case) simply removing them fixes
the problem and makes the test suite reliable.

Sometimes, when another process just happened to create a file
when we were setting up a watch, the new file wouldn't be noticed.

To prevent the event not being generated in this case, schedule
a directory rescan immediately after setting up a watch.

Fixes paulmillr#1112