Make a test more resilient against the host system

If the host system had $HOME/.cargo/config which configured a user name/email
then this test would fail because those would be prioritized over $USER.

Closes #514
Fix typos in `cargo build -h`
Update dependencies
Add --open flag to cargo doc
auto merge of #655 : ebfe/cargo/deps, r=alexcrichton

At least rust-encoding needs updating to compile with rust master.
auto merge of #631 : alexcrichton/cargo/issue-514, r=brson

If the host system had $HOME/.cargo/config which configured a user name/email
then this test would fail because those would be prioritized over $USER.

Closes #514
auto merge of #652 : tomaka/cargo/open-docs, r=alexcrichton

Opens the generated docs in a browser.

Since it's more a utility feature, I didn't write this in a robust way. There's no error if it fails to open a browser.
auto merge of #654 : ebfe/cargo/cargo-build-help, r=alexcrichton