Hello,

Following on from my recent post to add an unwind_dummy_id() method, 
this code adds architecture specific methods to handle the edge case of 
unwinding the sentinel frame's PC/ID.

While I'm pretty sure that the methods are needed, I'm not 100% certain 
of their interfaces.  The attached has:

	unwind_sentinel_id(arch, regcache, unwind_cache)

I'm wondering if, instead it should use something like:

	unwind_sentinel_id(arch, tpid, unwind_cache)

where a new method:

	tpid_regcache (tpid)

could be used to obtain the tpid's register cache.  I'm thinking this 
since, for the case of the i386, it may need the thread's state in 
addition to registers when determing the `pc'.

Anyway, I'm going to table this for a bit.
Andrew