Restore pageLabels compatibility.

[sciurius]

Before the last changes, pageLabel accepted style arguments roman, arabic, etc. In 2.042, it merely takes the first letter (provided it is a, d or r). In short, arabic now comes out as a (lowercase letters) instead of D (Decimal arabic numerals).

[ssimms]

Thanks! I've implemented a similar fix with the addition of a warning, as noted in the issue.