Update snakeyaml to 1.12; Adds BUKKIT-48

http://code.google.com/p/snakeyaml/wiki/changes
Issue 66 "Provide serialization with minimum layout change" is fixed in
snakeyaml 1.11 and addresses BUKKIT-48.

Another highlight is "Improve the error message when a TAB is used as
indentation"

Leaky: https://bukkit.atlassian.net/browse/BUKKIT-48