- exceptions_test: exceptions_test now succeeds, unless we're JITting.
  It fails due to a bug in llvm codegen having to do with definedness
  analysis; see comment in emitBBs in irgen.cpp.

- with_{class,functiondef}, try_{class,def}: Expose the same JIT bug
  that occurs in exceptions_test.

- try_return_finally: We used to flip an internal assert in
  compareKeyset when JITting this test, but it's fixed now.

- file_closed: Files have a `closed' attribute in Python, but not yet in
  Pyston.

- finally_except: Our CFG pass had some corner case bugs when nesting a
  try/finally inside a try/except. This checks they're fixed.

- try_continue: The CFG pass has a bug in its syntax error reporting.

- with_continue, try_continue: Checks that `with'/`try'/`finally' handle
  syntax errors properly.

- with_ctxclass_instance_attrs: Checks that we're accessing
  context-manager attributes on the context-manager's class, not the
  instance, when we run a `with'. As it turns out, our AST interpreter
  has a bug in ClsAttribute (I think) which means that we don't. Our JIT
  works ok, though.

- with_ctxclass_order_of_access: Checks that we're accessing
  context-manager attributes in the right order when we run a `with',
  which we are.

- with_file: Our `file' object runtime previously didn't support `with'
  properly. This checks that files work with `with'.