If one of locale-related variables set to a bad value in the user's
environment (like da_DK.ISO_8859-15 as opposed to da_DK.ISO8859-15 on
-CURRENT), perl ports cannot be built. While this condition clearly is
an operator error, it is still no excuse for the build failure.
Fix that by cleaning locale-related variables for configure and build
steps. No plist changes, no portrevision bump.
Reported by: Flemming Jacobsen <fj quite-at batmule maybe-dot dk>