Reorder YAML Representers to prefer customs; Adds BUKKIT-4680

By default, SnakeYAML will only represent a ConfigurationSerializable if
it does not extend a class already provided with a Representer (Number, 
List, Map, Set, Iterator, Object[], Date, Enum and Calendar).

Reordering the representers to place the custom classes first allows
a plugin author to explicitly override the default object serialization
when extending the default Representer classes.

http://code.google.com/p/snakeyaml/source/browse/src/main/java/org/yaml/
snakeyaml/representer/BaseRepresenter.java?name=v1.9#49