Don't warn the user when some DVD hooks fail.

Those hooks aren't critical for DVD playback and they often fail due to an incompatibility with NVIDIA drivers on some systems which unfortunately we can't fix on our side.

Refs: #3739.
VSFilter: Be more careful when using IMediaSample2 interface.
Sync Renderer: Remove some unneeded casts.
Add an option to prevent creating the external style file when saving a subtitle.
EVR renderers: Try to fix a deadlock.
Don't force any background color for the Shockwave graph.

This commit fixes #1747.
ISR: Render text subtitles relative to the video frame when in doubt.
Why "C:\tmp.srt"?
WebUI: Inform the web interface that no audio stream is available.
WebUI: Make use of new [hasaudio] info.
What the hell was intended here?!

Trying to make some sense of that code. Without much luck so far...
Fix: x86 and x64 versions conflicted over file associations.

4f465cf8b81f1da800b1bfc57cc48e317d24fbb5 was incomplete for Vista+.

This commit fixes #4064.
Auto mode for relative to.
Cosmetics: Use better IDs from the resource strings.