forbid extending sort K in the Java backend
fixed typo; added TODO comment; commented out user-substitution test temporarily
fixed the check; uncommented the user-substitution regression test
change K to KItem in samples
changed K to KItem in include
added the missing function attribute to substitution
changed K to KItem in tests
added check to forbid extending KList as well
changed K to KItem in tutorial
fixed copyright
fixed error message
merged with unified-builtins2
fixed imp-hoare
Update symbolic-calculus.k
Merge pull request #714 from yilongli/fixing-issue#708

forbid extending sort K in the Java backend