[Ada] tasking clean ups/improvements

[Arnaud Charlet <charlet at adacore dot com>]

Tested on i686-linux, committed on trunk.

Previously, the type System.Priority on AIX was limited to the range 0
.. 31. This met the language requirement that the type include at
least 30 values, but as the underlying threads implementation on the
target supports a wider range, it is possible to provide a wider range
to the user. This patch expands that range to 0 .. 126, allowing
tasking programs to use the entire range of priorities provided by the
system.

Similarly, the type System.Priority on Linux is extended to the range
0 .. 97.

Also implement support for PTHREAD_PRIO_PROTECT and PTHREAD_PRIO_INHERIT
under AIX (Ada equivalent is resp. pragma Locking_Policy
(Priority_Ceiling/Priority_Inheritance)).
For PTHREAD_PRIO_INHERIT, the value is different between AIX < 5.3 and
5.3, so we introduce a function which will query the OS version number
at run-time the first time this function is called (if at all).

Finally, ACATS test cxc3001 on AIX 5 shows that the list of reserved signals
for this platform needs to be updated, which is confirmed by reading
/usr/include/sys/signal.h

2006-10-31  Arnaud Charlet  <charlet@adacore.com>
	    Jose Ruiz  <ruiz@adacore.com>

	* s-osinte-posix.adb, s-osinte-linux.ads, s-osinte-freebsd.adb, 
	s-osinte-freebsd.ads, s-osinte-solaris-posix.ads, s-osinte-hpux.ads, 
	s-osinte-darwin.adb, s-osinte-darwin.ads, s-osinte-lynxos-3.ads,
	s-osinte-lynxos-3.adb (To_Target_Priority): New function maps from
	System.Any_Priority to a POSIX priority on the target.

	* system-linux-ia64.ads: 
	Extend range of Priority types on Linux to use the whole range made
	available by the system.

	* s-osinte-aix.adb, s-osinte-aix.ads (To_Target_Priority): New
	function maps from System.Any_Priority to a POSIX priority on the
	target.
	(PTHREAD_PRIO_PROTECT): Set real value.
	(PTHREAD_PRIO_INHERIT): Now a function.
	(SIGCPUFAIL): New signal.
	(Reserved): Add SIGALRM1, SIGWAITING, SIGCPUFAIL, since these signals
	are documented as reserved by the OS.

	* system-aix.ads: Use the full range of priorities provided by the
	system on AIX.

	* s-taprop-posix.adb: Call new function To_Target_Priority.
	(Set_Priority): Take into account Task_Dispatching_Policy and
	Priority_Specific_Dispatching pragmas when determining if Round Robin
	must be used for scheduling the task.

	* system-linux-x86_64.ads, system-linux-x86.ads, 
	system-linux-ppc.ads: Extend range of Priority types on Linux to use
	the whole range made available by the system.

	* s-taprop-vms.adb, s-taprop-mingw.adb, s-taprop-irix.adb, 
	s-taprop-tru64.adb, s-taprop-linux.adb, s-taprop-hpux-dce.adb, 
	s-taprop-lynxos.adb (Finalize_TCB): invalidate the stack-check cache
	when deallocating the TCB in order to avoid potential references to
	deallocated data.
	(Set_Priority): Take into account Task_Dispatching_Policy and
	Priority_Specific_Dispatching pragmas when determining if Round Robin
	or FIFO within priorities must be used for scheduling the task.

	* s-taprop-vxworks.adb (Enter_Task): Store the user-level task id in
	the Thread field (to be used internally by the run-time system) and the
	kernel-level task id in the LWP field (to be used by the debugger).
	(Create_Task): Reorganize to unify the calls to taskSpawn into a single
	instance, and propagate the current task options to the spawned task.
	(Set_Priority): Take into account Priority_Specific_Dispatching pragmas.
	(Initialize): Set Round Robin dispatching when the corresponding pragma
	is in effect.

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