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This uses the version at commit 35c76bf (2015-12-08)
https://github.com/github/hub/commit/35c76bf91dc3d699173599464b9b41cb877ee440

Removes old completion setup that breaks with current _git and _hub completions.
Ruby is no longer required by hub; removes that test.
Does not define new completions for hub; they are now defined by hub itself.
Change the functions to use hub to create the repos on GitHub.
Add error checking to the functions.
Removes apparently-unused _github completion definition.

`hub` is crashing for me on a old CentOS setup with
"undefined method `shelljoin'".

On first use of the `git` function it is now checked if
`hub --version` returns successfully.

Add missing newlines at EOF. Remove redundant comment. Fix grammar in comment.

I've run into the issue where a stripped down container had no Ruby
installed, which caused `hub` to fail.

Therefore I've added an extra check to verify that `ruby` is in the
commands list before setting up this alias/function.