Update to Minecraft 1.6.2

No changes were required, except the usual number updates. Version is
now 2.4.13.
"Fix" a NPE

I don't know why this happens yet, but it crashes servers.
Properly fix the NPE
Correctly follow height limits for caves
Corrected liquid source generation
Merge pull request #176 from Brokkonaut/patch-1

Bugfixes for Cave generation height limits and liquid source generation
Fix for POMs... again
Merge remote-tracking branch 'upstream/master'