Don't rename a directory to a directory

Test by @EdShaw!

Closes #227
auto merge of #246 : alexcrichton/cargo/issue-227, r=wycats

Test by @EdShaw!

Closes #227
Filter the current package out of override paths

The current package being built should never be overridden, only its
dependencies.

Closes #225
Add `cargo new` to the `cargo help` message
auto merge of #248 : alexcrichton/cargo/issue-225, r=wycats

The current package being built should never be overridden, only its
dependencies.

Closes #225
Bootstrap cargo with cargo