Always return a file descriptor in sceIoOpenAsync.

Fixes #646.
Add a few missing sceDisplay syscalls.

Found in Lunar.
Implement sceDisplayWaitVblankStartMulti().

Fixes Falcom games running at too-fast framerates.
Show an FPS counter if ini option is true
Merge pull request #648 from unknownbrackets/io-minor

Always return a file descriptor in sceIoOpenAsync
Merge pull request #649 from unknownbrackets/display-multi

Implement sceDisplayWaitVblankStartMulti()
Show record high FPS
Merge pull request #650 from KentuckyCompass/fps_counter

Fps counter