pull super class valid check into helper method
fix small typo
skip invoke dynamic test for new backend until support added

the new backend doesn't even know how to say it can't do invokedynamic yet, so mark that test as pending
add some tests around assignment types, 1 working 2 pending

0ed0ed8a08d98f2ed8fcf69934bf76e60c5f7d2c made it so that

  a = b = c

is equivalent to

  b = c
  a = c

in terms of type inference.

This commit adds some tests around assignment/return edge cases
with primitives, since they must be explicitly converted in
bytecode.

A couple of them are pending. Essentially the problem is that if
the last expression in a method is of type X, but the method is
supposed to return Y where X can be widened to Y, the widening bit
isn't generated