Use the current file directory as default folder for the "Load Subtitles" dialog.

This commit fixes #2924.
Cosmetic: Use the MFC function for IShellItem creation from file paths.
Update changelog.
DVB Subtitles: Fix a crash with some subtitles streams.

Correctly follow the specs when parsing the display size.

This commit fixes #2931.
VideoRenderers: Move VSyncThread from DX9AllocatorPresenter to EVRAllocatorPresenter.

Only EVR-CP was using the thread, so it should be part of that class. This also gives us access to the RenderState which now prevents the thread from running while paused.

Fixes #593.
EVR-CP: Update commented out Multimedia Class Scheduler code.
And fix a typo.