added two whitespaces to make message_filter compile with c++11

more on this here: http://stackoverflow.com/questions/10329942/error-unable-to-find-string-literal-operator-slashes
strip leading slashes in resolve, and also any time a method is passed from tf to tf2 assert the leading slash is stripped as well.  tf::resolve with two arguments will end up with foo/bar instead of /foo/bar.  Fixes https://github.com/ros/geometry_experimental/issues/12