Update Polish translations and fix po4a errors in other languages' translations

Update Polish translations and fix po4a errors in other languages' translations

* po/pl.po: Apply some fixes suggested by Wiktor Wandachowicz.
* */pl.po: Consistently use Polish quotation marks in translations.
* man/{de.po, hu.po, sv.po}: Fix a few broken messages, that caused the
newest po4a to die with the `Unknown '<' or '>' sequence' error.