Rustpkg "ready for use" metabug

[graydon]

Rustpkg shipped in 0.6 essentially "not ready for use". It is not operating the way we want it to, long term, and we want to get it fixed up and usable by the community early in the 0.7 cycle. This is a tracking bug for major issues associated with its behavior.

Cross these issues off as you complete 'em

• use of pkgids (Rustpkg should operate on a URL-like pkgid #5679)
• crate inference (Rustpkg should infer crates to build #5680)
• extern mod for dependencies (Rustpkg should extract dependencies from extern mod statements. #5681)
• RUST_PATH (Rustpkg and rustc should use RUST_PATH env var to locate packages #5682)
• testing (Rustpkg needs to be testable #5683)
• VCS versions in pkgids and dependencies (Rustpkg should support versions integrated with a VCS #5684)
• using workcache (rustpkg should use workcache #7075)
• recursive dependencies (rustpkg test case for recursive dependencies #8524)
• installing to RUST_PATH (Use RUST_PATH to determine where to install to #7402)
• semantic versions (rustpkg should support semantic versions #8405)
• multi-crate packages (rustpkg: Test multi-crate packages #7240)
• package IDs pointing into a subdirectory (Allow package IDs to refer to the middle of a source repository #6408)