--solvers=smt-cvc4-cex
--solvers=smt-cvc4-proof

Update scala-smtlib with support for parsing special DefFunsRec

FiniteArray now takes an Expr for the length, a default
Expr, and a Map of defined Expr for some of its elements.
Adapt the rest of Leon to the new trees.

The PrettyPrinter tries to be a little bit smart about
how to print the array, only printing a few elements when the
array gets too big. The regression test produces an
huge array counter-example that used to lead to a crash of
Leon with the previous implementation of Array (fully represented
in memory).

Fixed SMTLIB for z3 target

reactivate tests for CVC4, if available. Remove non-linear testcase that
worked only on z3 (SumAndMax)

Update the build to reference the most recent version of
scala smt-lib and adapt the code to the new API.

Replace some use of NonStandardCommand by built-in standard
Commands of scala smt-lib.

 - Partial support for CVC4

- Implement smt and smt-z3/smt-cvc4 as options for --solvers

- Uses a main solver sources for verification/CLP, taking into account
  --solvers

- Implement Z3-SMT sets

- Add tests for Z3-SMT