o Remove the obscure tid command, because it does what the thread

o  Remove the obscure tid command, because it does what the thread
   command does, but worse.
o  Remove the obscure proc command, because it does what the thread
   command does, but not unambigously.
o  Move the PID to the extra thread info, where it makes sense and
   where it doesn't confuse users. The extra thread info holds some
   process information, to which the PID belongs.
o  Implement the to_find_new_threads target method by having it call
   the target beneath us if we're not using KVM. This makes sure that
   new threads are found when using the remote target.

o  Fix various core dump scenarios:
   -  Implement the to_files_info target method. Previously the
      'info target' command would cause a NULL pointer dereference.
   -  Don't assume there's a current thread. We're not initialized
      in all cases. This prevents a NULL pointer dereference.
   -  When we're not ussing KVM, have the to_xfer_memory target
      method call the target beneath us. This avoids calling into
      KVM with a NULL pointer.

MFC after: 1 week