Add limit option to ScriptableCollection.find method.

[sgkim126]

Currently, ScriptableCollection.find method retruns all matched result. This patch makes the method limit the number of the result.

For example, collection.find(query);' will return all result, but collection.find(query, 3);' will return only three elements of it.

Actually limit doesn't limit the number of document on network. It just reduces the conversion overhead.

[kseo]

Landed manually after cleaning up the commit log.