During the course of developing our pthread library (the NGPT pthread
library) it became clear we needed some kernel support for handling
signals.  This patch helps the library by redirecting all signals sent
to tasks in a thread group to the thread group leader.  It also defines
the tkill() system call so the library can signal a specific task if
necessary. 

Given that as far as I know NGPT is the only user of thread groups, and
that this change would benefit any other user of thread groups, I'm
submitting this for inclusion in the 2.5 kernel.

Note that this patch also adds support for sys_gettid() for the
architectures that don't have it.  While this could have been split into a
spearate patch, it would create conflicts since this patch also adds
sys_tkill(), so I felt it was cleaner to leave them together.

Dave McCracken

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Dave McCracken          IBM Linux Base Kernel Team      1-512-838-3059
dmccr@us.ibm.com                                        T/L   678-3059