Remove the note about CVC4 as the patch has been merged
Use a custom range for unconstrained arrays

This allows us to use non-standard expr widths and makes the SMT-LIB output
easier to read.
Fix a logic error when building candidate constraints with conditions

We were mistakenly testing the satisfiability of Cond -> E and Cond -> !E.
This is wrong; we need to test the validity of Cond -> !E and Cond -> E,
i.e. the satisfiability of !(Cond -> !E) and !(Cond -> E).