Merge branch 'cc/subprocess-handshake-missing-capabilities' into maint

Finishing touches to a topic already in 'master'.

* cc/subprocess-handshake-missing-capabilities:
  subprocess: loudly die when subprocess asks for an unsupported capability

sub-process.c

@@ -180,8 +180,8 @@ static int handshake_capabilities(struct child_process *process,
 			if (supported_capabilities)
 				*supported_capabilities |= capabilities[i].flag;
 		} else {
-			warning("subprocess '%s' requested unsupported capability '%s'",
-				process->argv[0], p);
+			die("subprocess '%s' requested unsupported capability '%s'",
+			    process->argv[0], p);
 		}
 	}