[codegen, testing] Tweaked ManglingClassWriter to try to recover reasonably
from classload failures in getCommonSuperClass. Relaxed the set of
method modifiers for which we are willing to generate code (anything
where the code generator doesn't care).
Added two test cases for method inheritance: One runs
Compiled12.inherit which the last checkin permitted to typecheck.
The second is TreapAndTest which runs a simple monomorphic Treap
implementation through its paces.
TreapAndTest is, at about 350LOC, the largest thing we've compiled
to date. It's also the first program to do serious data-structure
manipulation (rather than pushing numbers, strings, and small objects
around).
