The main changes are twofold:
* Buffer flipping is now controlled by the m_screen_can_set_buffer flag
in WSCompositor. This flag, in turn, is impacted by m_can_set_buffer
flag, in WSScreen. m_can_set_buffer is set in the WSScreen constructor
by checking the return value of fb_set_buffer. If the framebuffer
supports this operation, it will succeed, and we record this fact. This
information is then used by WSCompositor to set its own
m_screen_can_set_buffer flag.
* WSScreen now only requests a resolution change of the framebuffer. The
driver itself is ultimately responsible for what resolution or mode is
actually set, so WSScreen has to read the response from that request,
and has no choice but to accept the answer. This allows the driver to
choose a "close enough" value to what was requested, or simply ignore
it.
The result of this is that there is no special configuration necessary
for WindowServer to work with reduced-capability framebuffer devices.
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