*** MERGE TO STABLE BRANCH ***


Surprisingly large delta to make rebindable names work properly.
I was sloppily not checking the type of the user-supplied name,
and Ashley Yakeley's first experiment showed up the problem!

Solution: typechecker has to check both the 'standard' name and
the 'user' name and check the latter has a type compatible with the
former.

The main comment is with Inst.tcSyntaxName (a new function).