around CPU access to the framebuffer. This allows the hardware to set
up swappers to deal with endianness, or to tell EXA to move the pixmap
out to framebuffer if insufficient swappers are available (note: must
not fail on front buffer!).
Submitted by: benh
Now, if either source or dest were in framebuffer, try to get both
there, but prefer system memory for both otherwise. Required making
exaasync.c go through the try-acceleration path. This significantly
improves window resizing under composite, because previously the
pattern of creating a new pixmap and copying default contents from the
screen caused a fallback every time due to the new destination pixmap
being in system memory.
