[Xenomai-core] u_mode and condvar fixes.

[Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>]

Hi,

I pushed the changes fixing the u_mode (taken from Jan, slightly
modified) and condvar stuff (not entirely taken from Jan's changes), as
well as the modifications coming from Philippe's branch.

However, two questions remain open:
- as in Jan's original patch, the u_mode stuff tests the presence of the
new syscall by testing whether it returns -ENOSYS. Now that we have the
vdso, I wonder if we should not use a vdso bit for this. This would give
us a systematic way of testing such syscalls extension.
- the condvar fix only fixes the general case, using errno, it does not
add any new syscall. I am not entirely convinced we really need to add
new syscalls. In fact we could use special values in the existing ones.
Or have access in kernel-space to the a process' vdso flags, allowing to
adapt according to these flags. I am simply wondering what is the
cleanest way.

What do you think?
Thanks in advance.

-- 
					    Gilles.