Add assertIsInstance to FlaskTestCase on 2.6
Add assertIsInstance to FlaskTestCase on 2.6

This fixes an error in ConfigTestCase.test_custom_config_class

TylerB24890/flask,grayswand1r/flask,sam-tsai/flask,wtorcasoGB/flask,jenalgit/flask,fkazimierczak/flask,rawrgulmuffins/flask,artleaf/flask,xiaoshaozi52/flask,horica-ionescu/flask,raven47git/flask,chenrenyi/flask,dawran6/flask,fengsp/flask,drewja/flask,jstacoder/flask,mysweet/flask,auready/flask,tony/flask,justanr/flask,GavinCruise/flask,liaoqingwei/flask,chuijiaolianying/flask,bodefuwa/flask,Faiz7412/flask,raven47git/flask,mitchfriedman/flask,flamelizard/flask,treedledee/flask,JingZhou0404/flask,sonnyhu/flask,justanr/flask,zoyanhui/flask,cliu-aa/flask,garaden/flask,xujianhai/flask,happyspace/flask,antsar/flask,raven47git/flask,flabe81/flask,artleaf/flask,wldtyp/flask,karlw00t/flask,visaxin/flask,kuhli/flask,jawed123/flask,Papa2k15/flask,jstacoder/flask,VShangxiao/flask,AndreaEdwards/flask,horica-ionescu/flask,q1ang/flask,happyspace/flask,WSDC-NITWarangal/flask,tristanfisher/flask,AvivC/flask,Parkayun/flask,SsangYoon/Flask,nju520/flask,TylerB24890/flask,cliu-aa/flask,kyle-sorensen/flask,jawed123/flask,edcomstock/flask,karlw00t/flask,sam-tsai/flask,abdulbaqi/flask,margguo/flask,gbolahanalade/flask,suppandi/flask,liaoqingwei/flask,Freebird2014/flask,jonatanblue/flask,mAzurkovic/flask,ffsdmad/flask,kuku940/flask,fevxie/flask,HeyItsAlan/flask,oculardexterity/flask,robertglen/flask,chenke91/flask,flamelizard/flask,fkazimierczak/flask,xiaoshaozi52/flask,DesQi/flask,niima/flask,visaxin/flask,tripathi62674/flask,ffsdmad/flask,algoStruct/flask,brianbeale/flask,EasonYi/flask,GavinCruise/flask,ankurpandey/flask,beni55/flask,anujk3/flask,skmezanul/flask,jonieli/flask,VShangxiao/flask,alexwidener/flask,homeworkprod/flask,chuijiaolianying/flask,s7v7nislands/flask,wangjun/flask,pinkpet/flask,nju520/flask,gilesburnfield/flask,ankurpandey/flask,vishnugonela/flask,chenke91/flask,pallets/flask,GavinCruise/flask,EasonYi/flask,hoatle/flask,visaxin/flask,alanhamlett/flask,Ricardo666666/flask,felipefuka/flask,elelianghh/flask,sage417/flask,rawrgulmuffins/flask,xujianhai/flask,drewja/flask,rollingstone/flask,aniketshukla/flask,ankravch/flask,jonieli/flask,arvinls/flask,adrianmoisey/cptdevops,ghhong1986/flask,fengsp/flask,jeezybrick/flask,stephaniemertz/flask,fanshaohua-fan/flask,jorpramo/flask,mrdon/flask,blankme/flask,lord63-forks/flask,jorpramo/flask,moluzhang/flask,wtorcasoGB/flask,liukaijv/flask,iamantee/flask,tangfeng1/flask,blankme/flask,HeyItsAlan/flask,kyle-sorensen/flask,iamantee/flask,gaomingnudt/gm-flask2.0,JamesTFarrington/flask,zoyanhui/flask,moluzhang/flask,theo-l/flask,niima/flask,tjxiter/flask,abdulbaqi/flask,szymonm/flask,liuyi1112/flask,LonglyCode/flask,gangeshwark/flask,liaoqingwei/flask,chenke91/flask,WSDC-NITWarangal/flask,Endika/flask,AndreaEdwards/flask,lyn233/flask,postelin/flask,treedledee/flask,fkazimierczak/flask,zailushangde/flask,onetinyr/flask,Papa2k15/flask,hoatle/flask,lord63-forks/flask,warm200/flask,cgvarela/flask,hyunchel/flask,chenrenyi/flask,jenalgit/flask,VShangxiao/flask,tripathi62674/flask,rollingstone/flask,s7v7nislands/flask,Freebird2014/flask,cgvarela/flask,qinfengsuiyu/flask,mitchfriedman/flask,ABaldwinHunter/flask-clone-classic,ZacariasBendeck/flask,mitsuhiko/flask,mrdon/flask,tcnoviembre2013/flask,ZacariasBendeck/flask,wangjun/flask,vivekanand1101/flask,Faiz7412/flask,SsangYoon/Flask,pledo/flask,SsangYoon/Flask,gangeshwark/flask,ABaldwinHunter/flask-clone-classic,felipefuka/flask,onetinyr/flask,vishnugonela/flask,sage417/flask,alexwidener/flask,luzzyzhang/flask,bluedazzle/flask,luvten/flask,jiimaho/flask,nZac/flask,tony/flask,s7v7nislands/flask,liuyi1112/flask,auready/flask,zailushangde/flask,skmezanul/flask,oculardexterity/flask,bluedazzle/flask,justanr/flask,wilbert-abreu/flask,q1ang/flask,XGiton/flask,tjxiter/flask,gangeshwark/flask,huwenhui/flask,godfreyy/flask,hyunchel/flask,wtl-zju/flask,postelin/flask,wilbert-abreu/flask,anujk3/flask,tangfeng1/flask,chuijiaolianying/flask,LonglyCode/flask,algoStruct/flask,aniketshukla/flask,mysweet/flask,ezequielo/flask,edcomstock/flask,pxzhenren/flask,huwenhui/flask,ryandvill/flask,szymonm/flask,cheesecake4392/flask,grayswand1r/flask,mujiatong/flask,Parkayun/flask,cheesecake4392/flask,ryandvill/flask,happyspace/flask,wtl-zju/flask,mitsuhiko/flask,pledo/flask,elelianghh/flask,DesQi/flask,kuhli/flask,nZac/flask,dominjune/flask,godfreyy/flask,postelin/flask,jeezybrick/flask,liukaijv/flask,mujiatong/flask,arvinls/flask,kuku940/flask,mrdon/flask,XGiton/flask,fanshaohua-fan/flask,godfreyy/flask,ankurpandey/flask,pinkpet/flask,karen-wang/flask,dawran6/flask,AndreaEdwards/flask,homeworkprod/flask,lynget/flask,pallets/flask,antsar/flask,jstacoder/flask,algoStruct/flask,nwags/flask,jorpramo/flask,Eagles2F/flask,gbolahanalade/flask,JingZhou0404/flask,tangfeng1/flask,mrdon/flask,RohithKP/flask,robertglen/flask,sonnyhu/flask,vishnugonela/flask,JamesTFarrington/flask,sixpi/flask,suppandi/flask,nwags/flask,EasonYi/flask,mAzurkovic/flask,warm200/flask,ryandvill/flask,ghhong1986/flask,oculardexterity/flask,dhruvsrivastava/flask,beni55/flask,sixpi/flask,anujk3/flask,alanhamlett/flask,Endika/flask,jiimaho/flask,lynget/flask,lalinsky/flask,wldtyp/flask,szymonm/flask,onetinyr/flask,nju520/flask,stephaniemertz/flask,ankravch/flask,adrianmoisey/cptdevops,bodefuwa/flask,Eagles2F/flask,garaden/flask,Ricardo666666/flask,wudafucode/flask,suppandi/flask,Ricardo666666/flask,qinfengsuiyu/flask,liuyi1112/flask,theo-l/flask,jonieli/flask,RohithKP/flask,AvivC/flask,lalinsky/flask,artleaf/flask,tcnoviembre2013/flask,pxzhenren/flask,TylerB24890/flask,Faiz7412/flask,margguo/flask,ezequielo/flask,ezequielo/flask,vivekanand1101/flask,luvten/flask,jonatanblue/flask,dominjune/flask,flabe81/flask,wudafucode/flask,luzzyzhang/flask,alanhamlett/flask,karen-wang/flask,karen-wang/flask,gilesburnfield/flask,tristanfisher/flask,dhruvsrivastava/flask,gaomingnudt/gm-flask2.0,brianbeale/flask,warm200/flask,kyle-sorensen/flask,jenalgit/flask,lyn233/flask,drewja/flask,pallets/flask,fevxie/flask