Fix layout
[Fix #487] Do not recenter after error list navigation

Preserve the position if the user is inside the error list
Properly pass package names to errcheck

Work around https://github.com/kisielk/errcheck/issues/45
Fix comment

[ci skip]
Fix indentation
Improve docstring

[ci skip]
[Fix #492] Do not needlessly recenter the error list

Only recenter if there are really some errors to move into the visible
part of the window.
Force-install all APT packages

It's a throw-away testing VM, so this won't do no harm, and avoids
hassles with broken upstream repos.  CFEngine, looking at you here!

See #496
Force-update the cache
Fix contribution requirements for provisioning

Thanks, @Wilfred

[ci skip]
[Fix #497] Handle empty messages from Clang
Fix style

[ci skip]
Bump Cask version
Fix Javascript test cases
Install js-yaml first
[Fix #398] Make minimum error level for navigation customizable
Allow nil value for error level
Change default to nil
Document the new option
Improve helper macro for navigation tests