The get_task_regs() call now accepts a pointer on a function that
is to keep obtained registers somwehere.

In CRIU case this "somewhere" is CoreEntry, for generic compel
user we'll need to add simple memcpy()-s to the library itself.
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>