This patch changes the interface of Nitpicker to support dynamically
dimensioned virtual frame buffers. This solves two problems:
First, it enables a client to create a connection to nitpicker without
donating much session quota in advance. The old interface required each
screen-size-dependent client to donate as much memory as needed to
allocate a screen-sized virtual framebuffer. For clients that are
interested int the screen size but cover just a small portion of the
screen (e.g., a banner, a menu, an applet that sits in the screen
corner), this overprovisioning is painful. The new interface allows such
clients to upgrade the session quota for an existing session as needed.
Second, because each nitpicker session used to have a virtual frame
buffer with a fixed size over the lifetime of the session, a client that
wanted to implement a variable-sized window had to either vastly
overprovide resources (by opening a session as large as the screen just
in order to be prepared for the worst case of a maximized window), or it
had to replace the session by a new one (thereby discarding the stacking
order of the old views) each time the window changes its dimensions. The
new interface accommodates such clients much better.
As a preliminary step for working on issue #11, this patch revisits the
'Framebuffer::info' RPC call. Instead of using C-style out paramters,
the new 'mode()' RPC call returns the mode information as an object of
type 'Mode'. Consequently, mode-specific functions such as
'bytes_per_pixel' have been moved to the new 'Framebuffer::Mode' class.
