Removal of scala-xml internal APIs

[Matt Farmer]

Hey all -

I think this has been known for a bit but we've been depending on some internal scala-xml api's that we're not supposed to use directly.

I am not merging this today - I want to do more testing, but I'd like other folks to kick the tires on it as well and let me know how it goes. :) 

https://github.com/lift/framework/pull/2050