Postgres single connections will no longer leak

Some users were experiencing problems with Postgres connections leaking when
they didn't enable pooling. This commit should fix the problem.

- In prototype.disconnect() we now properly call this.client.end with
  this.client.end.bind(this.client) (as shown in the node-postgres wiki).
- We no longer check for readyForQuery on this.client as that value may not
  always be populated by node-postgres (possibly a bug on node-postgres).

This should close https://github.com/sequelize/sequelize/issues/859

lib/dialects/postgres/connector-manager.js

@@ -116,7 +116,7 @@ module.exports = (function() {
       } else {
       } else {
         done && done()
         done && done()
         self.client = null
         self.client = null
-        emitter.emit('success', done)
+        emitter.emit('success')
       }
       }
     }
     }
 
 
@@ -124,7 +124,7 @@ module.exports = (function() {
       // acquire client from pool
       // acquire client from pool
       this.pg.connect(uri, connectCallback)
       this.pg.connect(uri, connectCallback)
     } else {
     } else {
-      if (!!this.client && this.client.readyForQuery === true) {
+      if (!!this.client) {
         connectCallback(null, this.client)
         connectCallback(null, this.client)
       } else {
       } else {
         //create one-off client
         //create one-off client
@@ -142,10 +142,9 @@ module.exports = (function() {
     }
     }
 
 
     if (this.client) {
     if (this.client) {
-      this.client.end()
+      this.client.end.bind(this.client)
     }
     }
 
 
-    this.client = null
     this.isConnecting = false
     this.isConnecting = false
     this.isConnected  = false
     this.isConnected  = false
   }
   }