Vars used for unique naming in place of Symbols

[Reid D McKenzie]

Clojure supports the use of Vars as values. Vars however are both more awkward to work with in terms of extracting name information, and are bart of the complected naming and binding system which Oxcart seeks to escape. Consequently, rather than using raw Var values to name Symbols and program values, Oxcart passes should be using namespace qualified symbols and all the def analysis passes should make appropriate transitions.

This is somewhat related to #13