Domain core-dumping fixes

Domain core-dumping fixes

The code was attempting to use the domain's current number of pages
(info.nr_pages) as a maximum index.  We then walk the memory map and
can easily over-write past the end of the nr_pages-sized array, if the
domain has more pages mapped in than earlier (live dump).  Restrict
ourselves to the current number of pages.

Also fix the dump core method in xend to actually implement the crash
and live options.  In particular this means that xend clients other
than xm now get non-live dumps by default.

Signed-off-by: John Levon <john.levon@sun.com>