Fixed missing transparency on upscaled textures

Textures with diagonal patterns were treated as opaque after resizing
Images upscaled by hqNx were affected mostly by this issue

http://forum.drdteam.org/viewtopic.php?f=24&t=5370
http://zandronum.com/tracker/view.php?id=269
http://zandronum.com/tracker/view.php?id=315
Merge pull request #15 from alexey-lysiuk/fix_upscale_transparency

Fixed missing transparency on upscaled textures
Merge branch 'master' of https://github.com/rheit/zdoom
Merge branch 'master' of https://github.com/rheit/zdoom
- add some compatibility settings to fix rendering glitches in BTSX_E1 MAP12.
- fix a render glitch with Back to Saturn X MAP06: Do not flood missing upper and lower textures with the backsector's flat if that backsector is malformed (i.e. has no area.)
- fixed: When applying Boom's Transfer_Heights effect to a sector, gl_FakeFlat needs to remove all portals from the original sector planes that are being replaced in the sector copy.
Merge branch 'master' of https://github.com/rheit/zdoom
Merge branch 'master' of https://github.com/coelckers/gzdoom into gz_osx