Tracking issue: Release a new cage

[emk]

We have a number of cage patches that people would like to have merged and released soon. These include:

• [x] We need to make sure that cage builds without errors. Any takers?
• [x] #74: --no-deps. Needs confirmation from @dkastner.
• [x] #70: Strip build except when needed. Requires final fixup from @camjackson, merge from @emk.
• [x] #75: Needs a PR updating Cargo.toml to use the new compose_yml release (0.0.49?). @camjackson, are you interested?
• [x] #78 Fix beta build (waiting to see if Travis is green)

[camjackson]

Yep, I'll bump the compose_yml version. I'll make sure there are no build errors along the way - is that what the first item refers to?

[camjackson]

PR is ready for the compose upgrade.

WRT cage building without errors, looking at the Travis logs for my PR:

• Stable Linux seems like a clean build, other than the rustfmt diff.

• Stable MacOS is mostly a clean build, except for these lines right at the end:

  changes detected, packing new archive
  .
  <Cut several lines of ...>
  .
  running `casher push` took longer than 180 seconds and has been aborted
  
  Done. Your build exited with 0.
  /Users/travis/.travis/job_stages: line 166: shell_session_update: command not found

• Beta Linux failed after getting stuck on Initializing pod 'db'
• Nightly Linux is failing with a whole bunch of clippy errors.

[emk]

We're getting close. Mostly, I'm just blocked on the code review for #70 and figuring out what's broken on CI.

[camjackson]

Would it help if I rebased that branch onto master?

[emk]

OK, we're getting really close. I'm waiting on a revised PR for #70 from @camjackson, and to see if I've fixed cargo new as described in #78.

[emk]

OK, we've addressed everything we can here, and I've moved the build issue #78 to the 0.2.4 milestone. Thank you to everybody who helped!