[libunwind] adding address-space concept to libunwind

[David Mosberger]

I just checked in a fairly sizeable patch to add an address-space
concept to the libunwind API (see
http://unwind.bkbits.net:8080/libunwind/address@hidden).  The goal of this
patch is to more cleanly support multi-process unwinding.  It also
ends up to cleaning up the code nicely and is another step towards
supporting dynamically generated code.

As far as existing code is generated: the impact should be minimal.
For local unwinding, nothing changes and for remote unwinding, you
simply have to create a new address space via unw_create_addr_space()
before calling unw_init_remote() (note: unw_create_addr_space() has to
be called only once per address-space/process; after that, you can
call unw_init_remote() as many times as you want).

Comments welcome.

Next week, I hope to revise the call-back interface, which will affect
primarily acquire_unwind_info().  This change is also intended to
finally add support for dynamically generated code.

Enjoy,

        --david