Add check for slug when editing page (fixes #119)
Add check for slug when editing page (fixes #119)

KimGlazebrook/wagtail-experiment,davecranwell/wagtail,zerolab/wagtail,m-sanders/wagtail,mayapurmedia/wagtail,inonit/wagtail,davecranwell/wagtail,takeshineshiro/wagtail,hamsterbacke23/wagtail,Klaudit/wagtail,inonit/wagtail,taedori81/wagtail,iansprice/wagtail,zerolab/wagtail,serzans/wagtail,nilnvoid/wagtail,mayapurmedia/wagtail,nimasmi/wagtail,hanpama/wagtail,bjesus/wagtail,gogobook/wagtail,thenewguy/wagtail,benemery/wagtail,chrxr/wagtail,Tivix/wagtail,WQuanfeng/wagtail,rsalmaso/wagtail,nealtodd/wagtail,willcodefortea/wagtail,marctc/wagtail,rsalmaso/wagtail,jorge-marques/wagtail,takeflight/wagtail,takeflight/wagtail,JoshBarr/wagtail,hanpama/wagtail,wagtail/wagtail,mixxorz/wagtail,tangentlabs/wagtail,jordij/wagtail,torchbox/wagtail,JoshBarr/wagtail,Toshakins/wagtail,m-sanders/wagtail,dresiu/wagtail,nimasmi/wagtail,hamsterbacke23/wagtail,WQuanfeng/wagtail,darith27/wagtail,jorge-marques/wagtail,benjaoming/wagtail,zerolab/wagtail,nealtodd/wagtail,jordij/wagtail,100Shapes/wagtail,gasman/wagtail,KimGlazebrook/wagtail-experiment,rsalmaso/wagtail,jorge-marques/wagtail,nutztherookie/wagtail,quru/wagtail,rv816/wagtail,benemery/wagtail,janusnic/wagtail,iansprice/wagtail,nrsimha/wagtail,hamsterbacke23/wagtail,timorieber/wagtail,bjesus/wagtail,chimeno/wagtail,lojack/wagtail,mixxorz/wagtail,thenewguy/wagtail,nilnvoid/wagtail,takeshineshiro/wagtail,Pennebaker/wagtail,rjsproxy/wagtail,rsalmaso/wagtail,nimasmi/wagtail,taedori81/wagtail,inonit/wagtail,Toshakins/wagtail,Pennebaker/wagtail,KimGlazebrook/wagtail-experiment,WQuanfeng/wagtail,nilnvoid/wagtail,kurtrwall/wagtail,kurtrwall/wagtail,jnns/wagtail,Pennebaker/wagtail,mephizzle/wagtail,FlipperPA/wagtail,mayapurmedia/wagtail,marctc/wagtail,gogobook/wagtail,dresiu/wagtail,helenwarren/pied-wagtail,mixxorz/wagtail,mixxorz/wagtail,iho/wagtail,janusnic/wagtail,willcodefortea/wagtail,taedori81/wagtail,benjaoming/wagtail,Klaudit/wagtail,takeflight/wagtail,iho/wagtail,Toshakins/wagtail,tangentlabs/wagtail,gogobook/wagtail,timorieber/wagtail,iho/wagtail,marctc/wagtail,kaedroho/wagtail,jnns/wagtail,quru/wagtail,lojack/wagtail,100Shapes/wagtail,WQuanfeng/wagtail,Toshakins/wagtail,rsalmaso/wagtail,rv816/wagtail,janusnic/wagtail,nrsimha/wagtail,takeflight/wagtail,timorieber/wagtail,davecranwell/wagtail,Klaudit/wagtail,helenwarren/pied-wagtail,willcodefortea/wagtail,benemery/wagtail,chrxr/wagtail,mjec/wagtail,marctc/wagtail,stevenewey/wagtail,chimeno/wagtail,jordij/wagtail,FlipperPA/wagtail,thenewguy/wagtail,benjaoming/wagtail,bjesus/wagtail,Tivix/wagtail,inonit/wagtail,hanpama/wagtail,takeshineshiro/wagtail,dresiu/wagtail,hamsterbacke23/wagtail,JoshBarr/wagtail,jnns/wagtail,Tivix/wagtail,chimeno/wagtail,chrxr/wagtail,kaedroho/wagtail,bjesus/wagtail,JoshBarr/wagtail,mjec/wagtail,rjsproxy/wagtail,timorieber/wagtail,quru/wagtail,mikedingjan/wagtail,kurtw/wagtail,wagtail/wagtail,tangentlabs/wagtail,kaedroho/wagtail,lojack/wagtail,taedori81/wagtail,takeshineshiro/wagtail,zerolab/wagtail,nutztherookie/wagtail,stevenewey/wagtail,torchbox/wagtail,gasman/wagtail,gasman/wagtail,quru/wagtail,serzans/wagtail,torchbox/wagtail,mjec/wagtail,100Shapes/wagtail,jordij/wagtail,rv816/wagtail,iansprice/wagtail,willcodefortea/wagtail,jorge-marques/wagtail,rjsproxy/wagtail,nrsimha/wagtail,hanpama/wagtail,mikedingjan/wagtail,nealtodd/wagtail,iho/wagtail,thenewguy/wagtail,wagtail/wagtail,kaedroho/wagtail,kurtrwall/wagtail,kurtw/wagtail,Klaudit/wagtail,helenwarren/pied-wagtail,mephizzle/wagtail,nealtodd/wagtail,jnns/wagtail,mikedingjan/wagtail,benjaoming/wagtail,darith27/wagtail,thenewguy/wagtail,janusnic/wagtail,Pennebaker/wagtail,kaedroho/wagtail,m-sanders/wagtail,rjsproxy/wagtail,mephizzle/wagtail,mjec/wagtail,gasman/wagtail,serzans/wagtail,stevenewey/wagtail,torchbox/wagtail,FlipperPA/wagtail,rv816/wagtail,tangentlabs/wagtail,nilnvoid/wagtail,taedori81/wagtail,gogobook/wagtail,m-sanders/wagtail,darith27/wagtail,zerolab/wagtail,kurtw/wagtail,dresiu/wagtail,stevenewey/wagtail,nrsimha/wagtail,mephizzle/wagtail,kurtrwall/wagtail,mayapurmedia/wagtail,wagtail/wagtail,kurtw/wagtail,nutztherookie/wagtail,darith27/wagtail,Tivix/wagtail,nutztherookie/wagtail,gasman/wagtail,benemery/wagtail,dresiu/wagtail,KimGlazebrook/wagtail-experiment,serzans/wagtail,chimeno/wagtail,davecranwell/wagtail,chrxr/wagtail,nimasmi/wagtail,FlipperPA/wagtail,iansprice/wagtail,wagtail/wagtail,mixxorz/wagtail,jorge-marques/wagtail,chimeno/wagtail,mikedingjan/wagtail