Fix 'Error allocating texture' error message.

[verm]

This error is pretty obtuse and confuses users, it needs to be updated to let users know what's going on and possible solutions.

[verm]

Argh, this was completely changed in r3615.. However the new error messages aren't much better than the old one so the ticket is still valid.

We should give the users some options in trying to fix the issue.

[nielsm]

For reference, this is the current message:

Failed seeking video. The video will be closed because of this.
If you get this error regardless of which video file you use, and also if you use dummy video, Aegisub might not work with your graphics card's OpenGL driver.
Error message reported: %s

The %s is usually a more detailed message, most of the time "Error allocating texture" iirc.

How about just replacing the "failed seeking video" part with this:

Could not upload video frame to graphics card.

I think that points better at the problem. Of course we should also add some checking for horrible Win7 GL drivers and such.

[verm]

I think "Video operation failed" makes more sense and is something everyone would understand.

We should also throw a message in there about updating their graphics card drivers to see if it will fix the problem. As this is what we tell 100% of people who ask us.

[nielsm]

Changing to low priority because the changes in video rendering mean barely anyone should be getting these errors any longer.

[plorkyeran]

(In [3835]) Improve video operation errors somewhat. Updates #1020.

[plorkyeran]

(In [3836]) Merge error message changes in r3835 from trunk. Updates #1020.

[verm]

Closet his as fixed, we're in a string freeze now so the message isn't going to get any better.