Stops the whitescreen of death some users were having. Also "readds" the red-damage-bloody-screen-so-real. I'll get a screenshot in a bit.

Source of the bug: I changed the red screen to use BLEND_MULTIPLY. Due to a mistake I made, the white part in the middle was fully opaque, but since it was a multiply blend, that didn't matter. Turns out in software mode, MULTIPLY defaults to OVERLAY or something, so users in software mode were seeing a fully opaque, non-blended white screen rather than a slightly red tint. Nasty.

Also multiply was stupid. The red was barely noticeable in many cases. Against black like space or things you couldn't see, the red literally didn't even display. No idea why I was so insistent on using this.

Solution: Instead I'll use BLEND_ADD which works just fine in software mode. However, ADD can't add blackness, so I have to have a second layer of darkness on the edges. Also I made the red on the so real blood screen brighter and more intense because it looked kind of dumb. This will probably need to be toned down or even reverted but that's ok.
Merge pull request #2555 from MrPerson/whitescreen_on_software_fix

Stops the whitescreen of death some users were having. Also "readds" the red-damage-bloody-screen-so-real.