Fixing problems with collection names which have the same name as fun…

…ctions in native

If you have collection names which are identical to functions in the mongodb-native you will get in trouble with the changes on the db prototype (a37030a and 26d17aa).
This small fix changes the behaviour:
If you initialize collection names with the connect they will overwrite the prototype functions.
If you use the explicit collection() you will always get the collection and not the possible available prototype function.

index.js

@@ -242,7 +242,6 @@ Database.prototype.runCommand = function(opts, callback) {
 
 Database.prototype.collection = function(name) {
 	var self = this;
-	if (this[name]) return this[name];
 
 	var oncollection = thunky(function(callback) {
 		self._get(function(err, db) {
@@ -251,7 +250,7 @@ Database.prototype.collection = function(name) {
 		});
 	});
 
-	return this[name] = new Collection(oncollection);
+	return new Collection(oncollection);
 };
 
 forEachMethod(DRIVER_DB_PROTO, Database.prototype, function(methodName, fn) {
@@ -282,7 +281,7 @@ var connect = function(config, collections) {
 
 	collections = collections || config.collections || [];
 	collections.forEach(function(colName) {
-		that.collection(colName);
+		that[colName] = that.collection(colName);
 	});
 
 	return that;