Reduce SMTAffineTerm.cleanup calls.

Since SMTAffineTerms are now unified, we don't need to call SMTAffineTerm for
NamedAtom.equals.  This patch boosts performance on many benchmarks.
Feature additions for DeltaDebugger.

Users can specify the expected golden exit code via command line.  Then, the
delta debugger will not run an initial check but simply assume the golden exit
code is correct unless it is 0.  Furthermore, the input file is not copied into
the result file anymore.  Only true minimisations are copied.  Finally, fresh
variables are tracked in the input to avoid clashes of function symbol names.