Added the hasPhysics method to the Material class, to get the block that
are affected by gravity.
Merge branch 'material' of github.com:nitnelave/Bukkit

* 'material' of github.com:nitnelave/Bukkit:
  Added the hasPhysics method to the Material class, to get the block that are affected by gravity.
Added the hasGravity method to Blocks. Adds BUKKIT-3832

This PR provides a mean to check across updates if a block is affected by
gravity or not.

CB-1029 - https://github.com/Bukkit/CraftBukkit/pull/1029 - Unit test
Merge pull request #4 from nitnelave/material

Material