patch for action_view/paths PathSet#insert to make sure it applys appropriate cast

PathSet attempts to make sure that any path it is given to manage is cast to a Path object if it's a string. It's inherited Array#insert will allow you to insert a string into it, causing problems later in reload! (which calls reload! on all it's children, which is defined for paths but not strings.)

This patch makes sure that insert plays by the same rules as [], unshift, and other similar methods. Infact, somebody should find all the mutating methods of Array that accept strings as in put and make sure they are overridden in PathSet to perform casts.