add clarifying comment about how test_overriding relates to model inheritance
add clarifying comment about how test_overriding relates to model inheritance

kaedroho/wagtail,mikedingjan/wagtail,rjsproxy/wagtail,hanpama/wagtail,nealtodd/wagtail,rsalmaso/wagtail,jordij/wagtail,mixxorz/wagtail,torchbox/wagtail,mikedingjan/wagtail,torchbox/wagtail,kaedroho/wagtail,thenewguy/wagtail,hamsterbacke23/wagtail,hamsterbacke23/wagtail,iansprice/wagtail,rjsproxy/wagtail,FlipperPA/wagtail,mixxorz/wagtail,gasman/wagtail,gogobook/wagtail,zerolab/wagtail,wagtail/wagtail,darith27/wagtail,thenewguy/wagtail,kurtw/wagtail,nilnvoid/wagtail,davecranwell/wagtail,rv816/wagtail,benjaoming/wagtail,JoshBarr/wagtail,nutztherookie/wagtail,bjesus/wagtail,jordij/wagtail,darith27/wagtail,torchbox/wagtail,FlipperPA/wagtail,kaedroho/wagtail,kurtrwall/wagtail,Pennebaker/wagtail,mjec/wagtail,tangentlabs/wagtail,tangentlabs/wagtail,davecranwell/wagtail,nrsimha/wagtail,taedori81/wagtail,Tivix/wagtail,janusnic/wagtail,m-sanders/wagtail,jnns/wagtail,mixxorz/wagtail,KimGlazebrook/wagtail-experiment,nimasmi/wagtail,mephizzle/wagtail,rjsproxy/wagtail,tangentlabs/wagtail,Tivix/wagtail,chrxr/wagtail,jnns/wagtail,marctc/wagtail,JoshBarr/wagtail,mayapurmedia/wagtail,gogobook/wagtail,jnns/wagtail,WQuanfeng/wagtail,nimasmi/wagtail,iansprice/wagtail,timorieber/wagtail,takeflight/wagtail,bjesus/wagtail,nutztherookie/wagtail,serzans/wagtail,janusnic/wagtail,mephizzle/wagtail,rsalmaso/wagtail,hanpama/wagtail,WQuanfeng/wagtail,serzans/wagtail,iansprice/wagtail,kurtw/wagtail,thenewguy/wagtail,mikedingjan/wagtail,gasman/wagtail,taedori81/wagtail,wagtail/wagtail,thenewguy/wagtail,nrsimha/wagtail,nutztherookie/wagtail,mixxorz/wagtail,rv816/wagtail,davecranwell/wagtail,marctc/wagtail,mjec/wagtail,benjaoming/wagtail,rv816/wagtail,mjec/wagtail,hanpama/wagtail,jorge-marques/wagtail,takeshineshiro/wagtail,KimGlazebrook/wagtail-experiment,rsalmaso/wagtail,inonit/wagtail,stevenewey/wagtail,tangentlabs/wagtail,chimeno/wagtail,WQuanfeng/wagtail,jorge-marques/wagtail,Klaudit/wagtail,gogobook/wagtail,benjaoming/wagtail,WQuanfeng/wagtail,nilnvoid/wagtail,KimGlazebrook/wagtail-experiment,jordij/wagtail,quru/wagtail,chimeno/wagtail,nilnvoid/wagtail,KimGlazebrook/wagtail-experiment,kurtrwall/wagtail,thenewguy/wagtail,iho/wagtail,Pennebaker/wagtail,nealtodd/wagtail,quru/wagtail,bjesus/wagtail,Klaudit/wagtail,darith27/wagtail,FlipperPA/wagtail,nealtodd/wagtail,kurtrwall/wagtail,mayapurmedia/wagtail,rjsproxy/wagtail,takeshineshiro/wagtail,takeshineshiro/wagtail,stevenewey/wagtail,marctc/wagtail,takeshineshiro/wagtail,Pennebaker/wagtail,nilnvoid/wagtail,timorieber/wagtail,taedori81/wagtail,Klaudit/wagtail,chimeno/wagtail,rsalmaso/wagtail,benjaoming/wagtail,quru/wagtail,gogobook/wagtail,mephizzle/wagtail,m-sanders/wagtail,inonit/wagtail,iansprice/wagtail,jnns/wagtail,taedori81/wagtail,mayapurmedia/wagtail,stevenewey/wagtail,rsalmaso/wagtail,takeflight/wagtail,gasman/wagtail,nealtodd/wagtail,zerolab/wagtail,timorieber/wagtail,iho/wagtail,kurtw/wagtail,gasman/wagtail,mikedingjan/wagtail,Pennebaker/wagtail,rv816/wagtail,inonit/wagtail,FlipperPA/wagtail,dresiu/wagtail,wagtail/wagtail,zerolab/wagtail,nrsimha/wagtail,dresiu/wagtail,Toshakins/wagtail,hamsterbacke23/wagtail,mixxorz/wagtail,Toshakins/wagtail,kaedroho/wagtail,chrxr/wagtail,Tivix/wagtail,marctc/wagtail,Tivix/wagtail,darith27/wagtail,jorge-marques/wagtail,wagtail/wagtail,Toshakins/wagtail,jorge-marques/wagtail,nimasmi/wagtail,janusnic/wagtail,mayapurmedia/wagtail,m-sanders/wagtail,takeflight/wagtail,timorieber/wagtail,chimeno/wagtail,hanpama/wagtail,m-sanders/wagtail,inonit/wagtail,mjec/wagtail,stevenewey/wagtail,jordij/wagtail,chrxr/wagtail,chimeno/wagtail,nutztherookie/wagtail,serzans/wagtail,jorge-marques/wagtail,hamsterbacke23/wagtail,Toshakins/wagtail,kaedroho/wagtail,nrsimha/wagtail,taedori81/wagtail,zerolab/wagtail,gasman/wagtail,JoshBarr/wagtail,zerolab/wagtail,kurtw/wagtail,dresiu/wagtail,davecranwell/wagtail,iho/wagtail,chrxr/wagtail,mephizzle/wagtail,wagtail/wagtail,dresiu/wagtail,kurtrwall/wagtail,JoshBarr/wagtail,quru/wagtail,Klaudit/wagtail,nimasmi/wagtail,iho/wagtail,bjesus/wagtail,takeflight/wagtail,torchbox/wagtail,janusnic/wagtail,dresiu/wagtail,serzans/wagtail