Switch sequence comparisons to handle 32-bit sequence number wrap.

Switch sequence comparisons to handle 32-bit sequence number wrap.

Create a macro, XCB_SEQUENCE_COMPARE, that accepts two sequence numbers and
a comparison operator and correctly handles 32-bit wrap around.
Rewrite all ordered sequence number comparisons to use this macro.
Also, caught one error where a sequence was stored in a signed int variable.
Push out a GetInputFocus request when the sequence number does wrap at 32
bits so that applications cannot see sequence 0 (as that is an error
indicator).