Fixed BlockStringToType return value.

-1 was not a valid BLOCKTYPE and would not be recognized by the callers, ever.
CompoGenBiomal: Fixed signed vs unsigned comparison.
Replaced auto_ptr with unique_ptr.
BlockEntities: Removed the extra semicolon.
OctavedNoise: Unshadowed a local variable.
RidgedNoise: Replaced fabs with std::abs().
Minecart.h: Fixed integral conversion warning.
OctavedNoise: Another unshadowed local variable.
Chunk: Fixed same-name iterators.
Merge pull request #1619 from mc-server/WarningFixes

Warning fixes