Comments and a few minor changes to start event

knex.js

@@ -120,7 +120,10 @@ Knex.initialize = function(config) {
     Dialect = Clients[clientName]();
     client  = new Dialect(config);
 
-    // Passthrough all "query" events to the knex object.
+    // Passthrough all "start" and "query" events to the knex object.
+    client.on('start', function(obj) {
+      knex.emit('start', obj);
+    });
     client.on('query', function(obj) {
       knex.emit('query', obj);
     });

lib/runner.js

@@ -28,14 +28,34 @@ Runner.prototype.run = Promise.method(function() {
     .then(this.ensureConnection)
     .then(function(connection) {
       this.connection = connection;
+
+      // Emit a "start" event on both the builder and the client,
+      // allowing us to listen in on any events. We fire on the "client"
+      // before building the SQL, and on the builder after building the SQL
+      // in case we want to determine at how long it actually
+      // took to build the query.
       this.client.emit('start', this.builder);
-      this.builder.emit('start');
       var sql = this.builder.toSQL();
+      this.builder.emit('start', this.builder);
+
       if (_.isArray(sql)) {
         return this.queryArray(sql);
       }
       return this.query(sql);
     })
+
+    // If there are any "error" listeners, we fire an error event
+    // and then re-throw the error to be eventually handled by
+    // the promise chain. Useful if you're wrapping in a custom `Promise`.
+    .catch(function(err) {
+      if (this.builder._events.error) {
+        this.builder.emit('error', err);
+      }
+      throw err;
+    })
+
+    // Fire a single "end" event on the builder when
+    // all queries have successfully completed.
     .tap(function() {
       this.builder.emit('end');
     })