Pass the canonical signal name to the signal handler when it is invoked.

Pass the canonical signal name to the signal handler when it is invoked.

Prior to this change, when a signal handler was invoked, the signame passed
into the sub would be the name of the signal that was defined first via {}.
This meant that the handler had to either be aware of the duplicates and
handle things appropriately or it would be at the mercy of action at a
distance the handler might be unaware of.

This change assures a consistent signal name for now on. It should be
the first signal listed in $Config{sig_name}. Duplicates are listed
at the end.