Fix highlights for right-aligned bars.

Support for right-aligned bars was never added to the hover or highlight
code; only the actual bar drawing. We need to replicate that in the
other two places as well.

Resolves #1093.
Always simply default to center alignment.

Throwing an exception was overkill for such a limited-use option; we
should reserve those, and the file-size bytes they consume, for serious
cases only.
Updated credits for right-aligned bar fix.