core: add terabyte unit for size displayed
core: update German translations
core: add comments in translations for file size units
core: fix compilation warning on GNU/Hurd about unsigned long numbers
doc: fix examples of function string_format_size (plugin API reference)
core: update Japanese translations
Merge pull request #140 from l/translation_ja

core: update Japanese translations
doc: update Japanese auto-generated files
core: check that string is not NULL in function string_iconv