of SIGCHLD. The application can tell us whether it wants to own

of SIGCHLD.  The application can tell us whether it wants to own
SIGCHLD or not; if it does, it has to tell us about deaths of our
children.

Currently there are no callers in libxl which use these facilities.
All code in libxl which forks needs to be converted and libxl_fork
needse to be be abolished.

Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Committed-by: Ian Jackson <Ian.Jackson@eu.citrix.com>