* Add `love.graphics.isSupported("hdrcanvas")' to query whether the hardware
actually supports HDR canvases.
* Add optional third argument to `love.graphics.newCanvas(w,h, type)', where
`type' is one of "normal" or "hdr" and defaults to "normal". HDR canvases
use floating point that can have values > 1 to store pixels, allowing for
HDR rendering and other higher level lighting techniques when combined with
pixel effects.
* Add `canvas:getType()'.
Add a extern vec2 love_ScreenSize to the pixel effects that will
be (re)set upon PixelEffect::loadVolatile() and is used to flip
the fragment coordinate.
Unfixes #324 because canvases can have different dimensions than
the screen.
Add stencil attachment to framebuffer creation. Needed to remove depth
attachment to make it work, but that should not change anything, since depth
test is not enabled anyway. May need testing nonetheless.
Error reporting now resides in Graphics::newCanvas() instead of the
previous location wrap_newFramebuffer(). Changed error text for
"Error in implementation" to point to a possible fix.
rude
Alexander Szpakowski
vrld
Bart van Strien
Bill Meltsner