Add two upload warnings
Add two upload warnings

Adds the bad-prefix and the page-exists upload warnings.

Also add graceful handling of simulation mode when using chunked
uploading.

Change-Id: Ife628004680399e047a75d1443e1d7ac0a22aabf

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