Disable bits that test "MAGIC" environment variable.

Signed-off-by: Krzysztof Wilczynski <krzysztof.wilczynski@linux.com>
Rename project and/or repository to "go-magic" from "magic".

This is to avoid clashes with simple interface to libmagic for Ruby
Programming Language that I am working on in the same time.

Signed-off-by: Krzysztof Wilczynski <krzysztof.wilczynski@linux.com>