Don't override vanilla dropping mechanics for sand/gravel/anvils
Fixes http://dev.bukkit.org/bukkit-plugins/landslide/tickets/7-sand-gravel-doesnt-drop-if-block-above
Code cleanup
Version => 1.3.0-SNAPSHOT
Added support for bracing blocks
A block touching a bracing block won't slide.
Add support for sticky pistons holding blocks in place
Separate config for retracted and extended pistons
Also ensure that vanilla falling blocks (sand/gravel/anvils) are held