When updating for example the KDE Gear ports the most tedious and
time consuming part at the moment is chasing minor changes in the
localization part of the plist.
Make the framework support porters in that area, by providing a
new glob pattern PORTL10N and directory L10NDIR.
Analogously to PORTDOCS and PORTEXAMPLES this will auto-add
all files matching the corresponding glob PORTL10N to the plist
under L10NDIR.
L10NDIR defaults to ${PREFIX}/share/locale.
editors/kate: Example Conversion to using PORTL10N