[libunwind] dynamic unwind info update

[David Mosberger]

Just a quick note: I pushed an update into the bitkeeper tree which
fixes many bugs related to dynamic unwind info processing.  Also,
while at it, I fixed the code so you can specify a negative
region-length -N to indicate that the region covers the last N
instructions of the procedure (makes it possible to share the region
structure across procedures that have the same prolog/epilog).

I also added an (optional) get_proc_name() callback to the
unw_accessors_t structure and hooked it up in the ptrace-support
routines.

To see how this all hangs together, try something like this:

        $ make check
        $ tests/test-ptrace -v -t tests/ia64-test-dyn1

ia64-test-dyn1 generates a couple of routines at runtime and invokes
them.  test-ptrace single-steps through the test-program and then
does a backtrace after every instruction.  Though simple, that's
actually a pretty good way to verify that the unwind info is
correct.

Enjoy,

        --david