Minor windows fixes

Some trivial fixes...bigger fixes are pending and probably need some discussion.

21cfef6c45e6ab2220180e175cd3f92b7cc5d805: it converts windows paths (e.g. ros\core\mk) into *nix paths so that cmake doesn't fall over when it sees backslashes. Further discussion is at #355

c691275f56cb519ecabd1ab04d416c1e99d0dcad: haven't used it here, but will in a coming patch. Useful to have there at any rate.

10fb4ead188114f5156e6819c06e3755bf27aeeb: comments in the commit.