Cui

to work with assignable checking featuer; also modifying some assignable JML specs

Commits to MJ/org/multijava/mjc/. Changing spec of CValueType.valueEquals.

Commits to MJ/org/multijava/mjc. Some spec change.

Better assignable clause checking, but with the following problems. Because some of the preconditions are not evaluated with pre-state values while doing assignable clause checking, 71 tests in org.jmlspecs.models failed.

Branch for better assignable clause checking.

Committing better assignable clause checking on the assignable branch.

Replacing version accidentially committed to the main branch with this old version.