It used to be the case that we overwrite this->sync even if it was non-zero
when updating the texture, without deleting the sync object. If we update
faster than we render, the result would be leaking sync objects.
This commit ensures that sync objects are deleted when they are replaced.
This uses the same line sweep algorithm originally created to copy DXGI
textures to IVSHMEM to implement the copy from IVSHMEM to memory-mapped
pixel buffer objects.
The way things were handled in EGLTexture is not only very hard to
follow, but broken. This change set breaks up EGLTexture into a modular
design making it easier to implement the various versions.
Note that DMABUF is currently broken and needs to be re-implemented.
