Auto merge of #3137 - alexcrichton:bump-curl, r=brson

Update curl to track more error info

This hopefully will help out with https://github.com/rust-lang/cargo/issues/2464#issuecomment-250583778 by including https://github.com/alexcrichton/curl-rust/commit/07323ab5e868babb7a5437e8d2604761b913dab3 which should give us more information from libcurl