Update for portuguese translation

Hello

A debian user has contributed a update of portuguese translation. Even though I don't grok this language, the translation does indeed look better than the original. 

See http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=567179 for the bug and http://bugs.debian.org/cgi-bin/bugreport.cgi?msg=5;filename=pt.po;att=1;bug=567179 for the po file.

All the best
