add: support adding explicit files in subrepos Change the behavior of the add command such that explicit paths in subrepos are always added. This eliminates the previous behavior where if you called "hg add" for an explicit path in a subrepo without specifying the -S option, it would be silently ignored. If you specify patterns, or no arguments at all, the -S option will still be needed to activate recursion into subrepos.

tests: add test for add of explicit path in subrepo Add test coverage for the existing behavior where adds of explicit paths in subrepos are silently ignored. This is in preparation for changing the behavior of the add command to have better support for subrepos.