Improve Windows performance immensely

Busy-waiting for async reads (assuming system has 2 cores) improves the
performance due to numerous acks in ADB's protocol. Before we were waiting
100ms before every ack artificially slowing down the system.

If we need better performance on systems with one core, we should change
this to Sleep(1) (but even 1ms sleeping slows down `adb push`
considerably).
Fix persistent crashing with ZTE Open on Windows 8
Merge pull request #774 from bkase/windows-perf

Improve Windows performance immensely