Make frame timing more precise, add option for less lag

This adds an option to use alternate timing, which syncs up the game clock every 1ms when not fast forwarding.  This reduces potential input, network, and audio lag when the cpu is able to complete faster than realtime (common especially on PCs.)

However, it's slower, especially with multithreading off.  Which is why I'm leaving it as an option.  I haven't really tested it on Android.

Adds the following string (not sure if this is the best description...):
Force real clock sync (slower, less lag)

A more thorough description here:
https://github.com/hrydgard/ppsspp/issues/4020#issuecomment-44773145

At least in one game, there's been confirmation this improves input lag.

Outside this feature, this also makes all platforms use slightly more accurate frame timing (sub millisecond) where possible.  On Windows, this makes the fps read at 100% way more consistently (instead of jumping up and down by 0.1% from time to time.)

-[Unknown]