add support for stopping compile

app/coffee/CommandRunner.coffee

@@ -9,9 +9,27 @@ module.exports = CommandRunner =
 		logger.log project_id: project_id, command: command, directory: directory, "running command"
 		logger.warn "timeouts and sandboxing are not enabled with CommandRunner"
 
-		proc = spawn command[0], command.slice(1), stdio: "inherit", cwd: directory
+		# run command as detached process so it has its own process group (which can be killed if needed)
+		proc = spawn command[0], command.slice(1), stdio: "inherit", cwd: directory, detached: true
+
 		proc.on "error", (err)->
 			logger.err err:err, project_id:project_id, command: command, directory: directory, "error running command"
 			callback(err)
-		proc.on "close", () ->
-			callback()
+
+		proc.on "close", (code, signal) ->
+			logger.info code:code, signal:signal, project_id:project_id, "command exited"
+			if signal is 'SIGTERM' # signal from kill method below
+				err = new Error("terminated")
+				err.terminated = true
+				return callback(err)
+			else
+				callback()
+
+		return proc.pid # return process id to allow job to be killed if necessary
+
+	kill: (pid, callback = (error) ->) ->
+		try
+			process.kill -pid # kill all processes in group
+		catch err
+			return callback(err)
+		callback()