Adding or subtracting a number and itself

Over a year ago, I ran a check over Google code for two patterns:
- `x - x`
- `(x + x) / 2` (but probably even `x + x` is suspicious)

Results are in internal CL 49788955. I see some of the same kinds of things you see for `x == x` (e.g., `foo1.getX() - foo1.getX()` instead of `foo1.getX() - foo2.getX()`). I also see some people using bad date APIs that require January = 0, for which they write `1 - 1` for January, `12 - 1` for December, etc. There may be other patterns where we wouldn't want to do this. Maybe we can just throw out anything with literals?