Pagegenerators.py: make grep a recognised key of GeneratorFactory.handleArg()
Pagegenerators.py: make grep a recognised key of GeneratorFactory.handleArg()

Replace.py does not understand that "grep" is a pagegenerators key
and uses -grep:xxx arg as replacement.
[see  "# Read commandline parameters" section in main()]

Change-Id: Iabe5caae61f5fab3151c97ed1900678ece58e655

Darkdadaah/pywikibot-core,npdoty/pywikibot,jayvdb/pywikibot-core,happy5214/pywikibot-core,smalyshev/pywikibot-core,h4ck3rm1k3/pywikibot-core,VcamX/pywikibot-core,TridevGuha/pywikibot-core,xZise/pywikibot-core,valhallasw/pywikibot-core,magul/pywikibot-core,emijrp/pywikibot-core,wikimedia/pywikibot-core,hasteur/g13bot_tools_new,trishnaguha/pywikibot-core,wikimedia/pywikibot-core,Darkdadaah/pywikibot-core,darthbhyrava/pywikibot-local,hasteur/g13bot_tools_new,npdoty/pywikibot,happy5214/pywikibot-core,PersianWikipedia/pywikibot-core,icyflame/batman,jayvdb/pywikibot-core,magul/pywikibot-core,hasteur/g13bot_tools_new,h4ck3rm1k3/pywikibot-core