Merge the following changes from the internal Cisco repository:

[TonySamuels]

• Make tar -> tar.gz enhancement backwards compatible
• Allow propagating from multiple changed dependencies
• Add channels*

Note that between clippy seeming not to have been run on all code and the automatic update tool to edition 2018, there are several parts of the diffs with no functional changes.

*Channels are a lal feature equivalent to git's branches. The idea behind it is that some dependencies may have multiple branches (e.g. for specific versions, or for different operating systems) and the build target may depend on a specific branch. By adding channels, a new version can be pushed for the dependency for each branch, and they will not conflict. The exact mapping between a channel and git branches (or any other method) is left to the user and tools that work with lal.

[clux]

Do you need some access to commit in here? I can probably elevate you. Btw, any chances of getting individual commits rather than a large blob?

[TonySamuels]

I don't believe I have access, but am happy to do it this way anyway.

We've caught a few other changes we want made at the same time, I'll see about redoing this merge with commits once those are complete, but it depends on how much work it would be to strip out any internal files. I expect it won't be a problem.