Prevent changes to other options from removing . from AutomapHostsSuffixes

This happened because we changed AutomapHostsSuffixes to replace "."
with "", since a suffix of "" means "match everything."  But our
option handling code for CSV options likes to remove empty entries
when it re-parses stuff.

Instead, let "." remain ".", and treat it specially when we're
checking for a match.

Fixes bug 12509; bugfix on 0.2.0.1-alpha.