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This new lock will gradually substitute to the ugly one in the
relevant sections of code, particularly:

- anything related to PI/PP management for mutexes
- changing the scheduling parameters of a thread
- updating a thread's shared state and/or info bits

This is a crucial state in phasing out the ugly lock. Mutexes won't
work properly after this change is in, until the related code is
converted as well.
Signed-off-by: Philippe Gerum <rpm@xenomai.org>