More int type fixes and tests for drivers

Just pulled in nightly and got a whole bunch of errors like this:
```
error: cannot determine a type for this expression: cannot determine the type of this integer; add a suffix to specify the type explicitly
```

Not sure, may be this just a follow-up on rust-lang/rust#6023?
Yes, those must me signed, as `dx = x1-x0` may be less than zero as we discussed above. @errordeveloper, please fix and re-enable the 15,15 -> 0,0 test, it should work.

@bharrisau, thanks for catching that.