Use custom_name for file namespace
Use custom_name for file namespace

Right now '%s' % FILE object returns ':File:' instead of 'File'
causing this script to behave really bad by changing [[File:Foo.jpg]]
to [[:File::Bar.jpg]]

Change-Id: I699dbcf5474a683871f20c2d548924ce7bdb137b

wikimedia/pywikibot-core,hasteur/g13bot_tools_new,PersianWikipedia/pywikibot-core,hasteur/g13bot_tools_new,magul/pywikibot-core,jayvdb/pywikibot-core,npdoty/pywikibot,magul/pywikibot-core,npdoty/pywikibot,happy5214/pywikibot-core,hasteur/g13bot_tools_new,happy5214/pywikibot-core,Darkdadaah/pywikibot-core,Darkdadaah/pywikibot-core,jayvdb/pywikibot-core,h4ck3rm1k3/pywikibot-core,h4ck3rm1k3/pywikibot-core,wikimedia/pywikibot-core