Keep track of disc0:/ vs. disc0: in path parsing.

The difference matters and was getting lost.
Properly savestate umd0: references.
Remove a duplicate syscall entry.
Fail with an error in sceIoChdir for invalid dev.
Fail if the cwd is too long as well.
Return an error when there's no async op.

And generally improve error codes for async io poll/wait funcs.

Fixes #1790.
Fix crashes / bad errors when loading a file fails.
Merge pull request #1791 from unknownbrackets/io-async

Correct errors for async io, other io fixes
Merge pull request #1792 from unknownbrackets/windows-ui

Fix crashes / bad errors when loading a file fails
av_get_default_channel_layout returns int64_t

And one less signed/unsigned comparison warning.
Merge pull request #1794 from aquanull/patch-2

av_get_default_channel_layout returns int64_t
Fix menu command shortcut keys.
Remove old junk.
Merge pull request #1795 from aquanull/master

Fix Windows accelerators (menu command shortcuts) enabling/disabling
Fix loop problem in Three Kingdom VIII
Merge pull request #1797 from raven02/patch-13

Fix BGM loop problem in Three Kingdom VIII
-O2 wasn't taking effect. Improves performance significantly for Blackberry.
Increase max volume of sceAudioOutput2OutputBlocking.
Merge remote-tracking branch 'upstream/master' into fps2