Make RE_PLURALIZER non-greedy to fix parsing of weird (but valid) .po files

Needed to make .po containing plural forms like these work:
"Plural-Forms: nplurals=2; plural=(n != 1);Content-Type: text/plain; "
Merge pull request #31 from diox/non-greedy-plural-regexp

Make RE_PLURALIZER non-greedy to fix parsing of weird (but valid) .po files