By default when region is not active, both `downcase-region` (C-x C-l)
and `upcase-region` (C-x C-u) will operate on surrounding text in
different ways depending on major-mode. This has caught me off guard a
few times.
So let's replace them with safer `downcase-region-only` and
`upcase-region-only` functions which ONLY perform changes when the
region is active. And obviously changes are only applied to the text
within the region.