Rationalise debugger stuff in the tree.
Within Xen itself, remove PDB references and fold into domu_debug.
When domu_debug hits a breakpoint, it pauses all vcpus of the domain
and raises VIRQ_DEBUGGER (not VIRQ_PDB). The debugger in domain0 can
either poll pause status or bind to VIRQ_DEBUGGER. Before debugging
a breakpointed domain the debugger should issue PAUSEDOMAIN itself, or
it is not guaranteed to see paused state of the domain!
Outside Xen there's a new dir tools/debugger, containing gdb, pdb and
a new library libxendebug (used by pdb). I also think the ptrace
functions in libxc also ought to be moved out: either to libxendebug
or to a new library libxenptrace.
Signed-off-by: Keir Fraser <keir@xensource.com>