Checkpoint:
  Add a performance test for interface method calls
  Slight performance improvements to Is/As/Cast methods
Force-enable the 'run' button in test_runner because firefox saves form element states on reload.
Minor rearrangements of type ID machinery
Checkpoint:
  Add basic caching support for interface members.
Checkpoint:
  Locally cache interface members when they are members of an open generic type.
Update a test.
Checkpoint:
  Fix some bootstrap interface member implementations.
Fix the ListICollection test case.
Allow passing a string interface name as the first argument to .Overrides instead of an integral index, for cases where the integral index is unknown.