Commit b225fdc44d4b3d in my po branch adds a `needstranslation()`
PageSpec. It makes it easy to list pages that need translation work.
Please review. --[[intrigeri]]

> Looks good, cherry-picked. The only improvment I can 
> think of is that `needstranslation(50)` could match
> only pages less than 50% translated. --[[Joey]] 

>> This improvement has been implemented as 98cc946 in my po branch.
>> --[[intrigeri]]

[[!tag patch done]]
