chg: send SIGPIPE to server immediately when pager exits (issue5278) If the user press 'q' to leave the 'less' pager, it is expected to end the hg process immediately. We currently rely on SIGPIPE for this behavior. But SIGPIPE won't arrive if we don't write anything (like doing heavy computation, reading from network etc). If that happens, the user will feel that the hg process just hangs. The patch address the issue by adding a SIGCHLD signal handler and sends SIGPIPE to the server as soon as the pager exits. This is also an issue with hg's pager implementation.