* New normal form for arithmetic is in place.

* New normal form for arithmetic is in place.
* src/theory/arith/normal_form.{h,cpp} contains the description for the new
  normal form as well as utilities for dealing with the normal form.
* src/theory/arith/next_arith_rewriter.{h,cpp} contains the new rewriter.
  The new rewriter implements preRewrite() and postRewrite() for arithmetic.
* src/theory/arith/arith_rewriter.{h,cpp} have been removed.
* TheoryArith::rewrite() has been removed.
* Arithmetic with the new normal form outperforms the trunk where the branch
  occurred (-r797) on 46% of the examples in QF_LRA. (33% have no noticeable
  difference.) Some important optimizations are stilling pending to the code
  for handling the new normal form. (Bug 196.)