Function invocation not attached to any value in
a statement block should be kept for potential
side effects. The committed regression test
illustrates the issue.

Additionally, become consistent in the name XLang
in various files of Leon.

Eliminate MutableTyped from Expr's. Expr.getType is now a val.
Variables don't have a mutable type.
Separate representation of empty and nonempty Sets, Maps, Multisets, and Arrays.
Introduce more generic constructors/ extractors for these types.
Simplify Map builder in NAryOperator.
Deprecate some deprecated Expr's.
Represent String literals as Lists.
Make some tests consistent with typing limitations in Leon.

Adds a benchmark with many cool magic tricks with bits.
However, proving some of them is very costly and we
could potentially look at opportunities to make the proofs
go through faster.

Leon now matches Scala semantics of Int as 32 bits bit-vectors.
This commits modifies the semantics of IntLiteral to be treated
as 32 bits integer everywhere (solver, evaluator, ...).

Introduces a new literal type, InfiniteIntegerLiteral, representing
a natural integer. The front-end maps the use of BigInt to these
new trees, and the solver properly handles them as mathematical
integers.

The behaviour of many regression tests changes due to this new
semantics. In particular many of them now timeout because they
are no longer proving properties over mathematical integers. This
commit updates the tests to reflect this new semantics.