Add to description of "Newline strips trailing spaces"

Add description of interaction between this action and indentation
since it is not obvious.
Change signal used to kill executions to SIGTERM

The originally used SIGQUIT has problems:
1) see the deleted comment
2) some xterm alternatives ignore it, so they don't stop

Changed to SIGTERM which is the canonical "terminate" signal.

Removed associated unneeded ignore of SIGQUIT.