Fix bug #7150 (Switching projects or quitting sometimes pauses for several
seconds) - Don't let Directory try to clear its immediate childrens'
caches. If we've already visited the parent dir and then we visit one of
its children, that child would have no _content anymore and would resort to
a full index-walk to try to find its own immediate children. This is slow
to do many times, and redundant since we're already doing a full walk
anyway.
Code review: pass 'true' for another visitAll()-_clearCachedData() loop
that follows the same potentially-inefficient pattern. Ian & I can't figure
out when this code would ever be needed - receiving a change event for
something that's not watched is nearly impossible, and it won't have any
cached data to clear anyway. We should probably remove this code in the
future. See https://github.com/adobe/brackets/pull/7155#discussion_r10486221
& follow-on comments for more.
Merge pull request #7155 from adobe/pflynn/fix-slow-unwatch

Fix bug #7150 (Switching projects or quitting sometimes pauses for several seconds)