adapting Quickcheck_Prolog to latest changes

changing Quickcheck_Narrowing's main function to enumerate the depth instead upto the depth

adapting mutabelle; exporting more Quickcheck functions

making quickcheck's result value more formal; allowing more result information to be returned after timeout; adding output of timing information in quickcheck

changing timeout behaviour of quickcheck to proceed after command rather than failing; adding a test case for timeout

added Syntax.const_abs_tr' with proper eta_abs and Term.is_dependent; recovered printing of Hoare assign statements from 45d090186bbe;

tuned;