Fix mac nightly builds

Older versions of curl apparently don't peel off the query parameters when
looking up filenames, so make two copies of the search results file in hope that
curl will find one of them!
auto merge of #1057 : alexcrichton/cargo/fix-nightly, r=brson

Older versions of curl apparently don't peel off the query parameters when
looking up filenames, so make two copies of the search results file in hope that
curl will find one of them!