Partially implement software watchpoints.

Currently ugdb only supports a single watchpoint. Every $Z2 silently
deletes the previous one.

As for multiple wp's, it is not clear to me how to implement this
correctly (and afaics in any case this is nontrivial). I'll try to
summarize my questions and send email to archer list.

Multitracing is another problem, right now I have no idea how this
can work with multiple debuggers.

Question: can I use the "current->thread.trap_no == 1" check to figure
out reliably whether this SIGTRAP was triggered by TIF_SINGLESTEP ?

Oleg.