Auto merge of #1205 - alexcrichton:case-sensitivity, r=brson

All crates published will enter the index in an all-lowercase fashion. This is
done because the index may be checked out on case-insensitive filesystems and
its integrity needs to be preserved. When looking for a file in the index, a
crate's name is transformed to all lowercase, but the mentioned name in the
index is verified against the name queried to ensure that they match.

Closes rust-lang/crates.io#93
cc rust-lang/crates.io-index#1