match: fix visitdir for roots of includes I'm hoping to rewrite the matcher so excludes are handled by composition of one matcher with another matcher where the second matcher has only includes. For that to work, we need to make visitdir() to return 'all' for directory 'foo' for a '-I foo' matcher.

match: make subdirmatcher extend basematcher This makes the subdirmatcher not depend on the main matcher, giving us more freedom to modify that (specifically, it will lose it _always field in a while).

match: make basematcher._files a @propertycache This will make it easier to override in subclasses (otherwise the function @propertycache object will be replaced by the super-constructor call)..

match: extract base class for matchers We will soon start splitting up the current matcher class into more specialized classes, so we'll want a base class for all the things that don't vary much between different matchers.