Adding missing Unreachable branch for case on Char, Int.
Optimize Int and Char ite.

The check for and optimize if the choice is between two of the same concrete
value, or if the choice is between two of the same object.

Fixes IntShare opt test case.
Minor cleanup in usage of iteF and iteF_.
Implement Unreachable optimization for ite of Char, Int.

Because I had forgotten to.
Updated TODO to reflect deferal of sketch performance bug.