Add ProjectAres/CraftBukkit 1.5 prerelease mappings ('acb')

Generated from unofficial CraftBukkit mc-dev 1.5 update:

https://github.com/ProjectAres/
http://cdn.oc.tc/maven/org/bukkit/minecraft-server/1.5pre/minecraft-server-1.5pre.jar

Named with 'acb' in this repository to distinguish from mappings
to be generated from the official CraftBukkit mc-dev from the Bukkit
team, once available ('cb').