Terminate backend when query_timeout is reached

[gajus]

The current implementation simply leaves the backend to hang.

node-postgres/lib/client.js

Lines 480 to 509 in 60d8df6

	if (readTimeout) {
	queryCallback = query.callback
	readTimeoutTimer = setTimeout(() => {
	var error = new Error('Query read timeout')
	process.nextTick(() => {
	query.handleError(error, this.connection)
	})
	queryCallback(error)
	// we already returned an error,
	// just do nothing if query completes
	query.callback = () => {}
	// Remove from queue
	var index = this.queryQueue.indexOf(query)
	if (index > -1) {
	this.queryQueue.splice(index, 1)
	}
	this._pulseQueryQueue()
	}, readTimeout)
	query.callback = (err, res) => {
	clearTimeout(readTimeoutTimer)
	queryCallback(err, res)
	}
	}

This seems dangerous. A better solution would seem to be to issue pg_cancel_backend when client timeout is reached.