Initial 1.6.1 Update

This is very experimental! It compiles, it can let players login, bugs should be reported to http://issues.libigot.org

Changelog
- Updated all Spigot patches to match upstream
- Updated Bukkit/CraftBukkit base to match upstream
- Removed patches no longer needed (World Emulator and Diff Visibility patches)
- Updated and resolved conflicts in various patches