Linux DDE used to implement Linux spin locks based on 'dde_kit_lock'.
This works fine if a spin lock is initialized only once and used
infinitely. But if spin locks are initialized on-the-fly at a high rate,
each initialization causes the allocation of a new 'dde_kit_lock'.
Because in contrast to normal locks, spinlocks cannot be explicitly
destroyed, the spin-lock emulating locks are never freed. To solve the
leakage of locks, there seems to be no other way than to support the
semantics as expected by the Linux drivers. Hence, this patch introduces
a DDE Kit API for spin locks.
The new 'Slave_policy' and 'Slave' classes are built upon the existing
child framework. They support the implementation of scenarios where a
service is started as a child of the client. This is usefull for
employing an existing service implementation as a local utility or
plugin.
The 'mode_sigh' function allows the client to receive notifications
about server-side display-mode changes. To respond to such a signal, the
client can use the new 'release' function, which acknowledges the mode
change at the server and frees the original framebuffer dataspace. Via a
subsequent call of 'dataspace', a framebuffer dataspace corresponding to
the new mode can be obtained. Related to issue #11.
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.
