Fix - Allow properly-formatted path parameters to work (also fixes URL::to('/')'s output)

This fix allows properly-formatted path parameters (those beginning with a slash; e.g. "/path/to/page") to be used, without breaking past compatibility by still allowing ("path/to/page") to work. These path parameters are used in methods such as URL::to('/page'), Redirect::to('/page'), etc.

Also, because of how this change is done, it fixes an issue where the root site path was being output incorrectly by URL::to. URL::to('/') used to output `http://domain.com` (without a trailing slash), but now outputs `http://domain.com/` as it should for the root URL.

So with this we can use:
`Redirect::to('/')`
`Redirect::to('/about')` (this now works)
`Redirect::to('about')` (the old way still works)

`URL::to('/')` - `http://domain.com/` (now has the trailing slash for the root!)
`URL::to('/path/to/page')` - `http://domain.com/path/to/page` (this now works)
`URL::to('path/to/page')` - `http://domain.com/path/to/page` (the old way still works)