Warning removal.

[jief666]

I used assertions in case of downcasting. Changed some var type (like size_t instead of int, etc.). Changed DecompressZLib and DecompressBZ2 parameters because the underlying lib cannot handle decompressing size_t bytes.

I fixed warnings reported by :

• clang called within xcode
• clang called from command line
• gcc for linux 32 bits
• gcc for osx.

Thanks.