Fix non-idiomatic code
Cleanup indentation and comments
Wrap long line
Use custom format strings for with-demoted-errors

Makes it easier to identify the cause of an error in 24.4, and is still
compatible with earlier Emacsen, because literal strings are in
expression bodies.
Fix headline levels in test suite
Add tests for proper indentation of source/test code
Replace (should (not …)) with (should-not …)
Remove misleading comment

[ci skip]
Mock message calls during tests

Use shut-up to mock calls to message during test cases, instead of
inspecting the *Messages* buffer.  This is more reliable, and does not
involve global side-effects.
Fix Rubocop tests
Merge remote-tracking branch 'upstream/master'

Conflicts:
	flycheck.el