Support more selective recursive watching

[davidmorgan]

Feature request: give a way to watch [directory recursive contents - specified set of directories].

This looks really useful for cases where there is a nested temp or output directory, because such directory are much noisier than the ones we actually care about.

I guess I am also volunteering to have a look at implementing the feature :)

This is forked from #1728 as just selectively ignoring directories would also be a way to address the same problem.

[devoncarew]

This sounds valuable - being able to specify (via a pattern? a list of names? a callback?) - a set of sub-directories to not watch.

[davidmorgan]

I would use it ;)

[devoncarew]

I guess I am also volunteering to have a look at implementing the feature :)

There isn't a specific owner of watcher right now; please feel very much empowered to follow up w/ a PR.

[lrhn]

Have someone made a proper general "include/exclude filter" implementation we could use?

Rather than make something specialized and limited.