Fix two compile time const issues

Fix two compile time const issues

- For equality expressions, the operands do not have to be of same
  type. (Issue 1671)

- Truncating division is allowed for any numerical type, not just
  integer. (Issue 1780) Spec has been updated accordingly and
  co19 issue 106 filed to fix faulty test.
Committed: https://code.google.com/p/dart/source/detail?r=6059

[srdjan, 2012-03-30 18:41:00]

lgtm