ENH: special: stick with the current convention for hyp2f1 a=c=negative integer, and enable a corresponding mpmath test
ENH: special: stick with the current convention for hyp2f1 a=c=negative integer, and enable a corresponding mpmath test

Addresses #1149

sriki18/scipy,behzadnouri/scipy,fredrikw/scipy,andyfaff/scipy,nmayorov/scipy,behzadnouri/scipy,fredrikw/scipy,witcxc/scipy,cpaulik/scipy,njwilson23/scipy,mhogg/scipy,efiring/scipy,juliantaylor/scipy,person142/scipy,ndchorley/scipy,zerothi/scipy,ales-erjavec/scipy,jjhelmus/scipy,nmayorov/scipy,argriffing/scipy,matthew-brett/scipy,cpaulik/scipy,WarrenWeckesser/scipy,sriki18/scipy,zerothi/scipy,rmcgibbo/scipy,Stefan-Endres/scipy,felipebetancur/scipy,fernand/scipy,FRidh/scipy,dominicelse/scipy,fernand/scipy,nvoron23/scipy,nvoron23/scipy,lukauskas/scipy,Gillu13/scipy,pbrod/scipy,mortonjt/scipy,gdooper/scipy,vhaasteren/scipy,surhudm/scipy,sauliusl/scipy,grlee77/scipy,jjhelmus/scipy,mhogg/scipy,vigna/scipy,piyush0609/scipy,kleskjr/scipy,mdhaber/scipy,ortylp/scipy,vanpact/scipy,surhudm/scipy,lhilt/scipy,richardotis/scipy,surhudm/scipy,nvoron23/scipy,jonycgn/scipy,kleskjr/scipy,Shaswat27/scipy,pnedunuri/scipy,giorgiop/scipy,pbrod/scipy,larsmans/scipy,grlee77/scipy,jor-/scipy,Newman101/scipy,dch312/scipy,pizzathief/scipy,WillieMaddox/scipy,sauliusl/scipy,mingwpy/scipy,vberaudi/scipy,dominicelse/scipy,anntzer/scipy,anielsen001/scipy,hainm/scipy,ales-erjavec/scipy,nonhermitian/scipy,matthewalbani/scipy,giorgiop/scipy,andyfaff/scipy,gef756/scipy,ChanderG/scipy,lhilt/scipy,sargas/scipy,efiring/scipy,Gillu13/scipy,andim/scipy,niknow/scipy,niknow/scipy,lukauskas/scipy,giorgiop/scipy,josephcslater/scipy,jsilter/scipy,josephcslater/scipy,larsmans/scipy,gertingold/scipy,niknow/scipy,lukauskas/scipy,haudren/scipy,Eric89GXL/scipy,fredrikw/scipy,Eric89GXL/scipy,ales-erjavec/scipy,e-q/scipy,jakevdp/scipy,jamestwebber/scipy,WillieMaddox/scipy,zerothi/scipy,futurulus/scipy,Stefan-Endres/scipy,richardotis/scipy,dch312/scipy,nonhermitian/scipy,piyush0609/scipy,vberaudi/scipy,cpaulik/scipy,argriffing/scipy,aarchiba/scipy,witcxc/scipy,njwilson23/scipy,Kamp9/scipy,ogrisel/scipy,person142/scipy,Eric89GXL/scipy,jamestwebber/scipy,zxsted/scipy,cpaulik/scipy,lhilt/scipy,FRidh/scipy,mortada/scipy,mortada/scipy,matthew-brett/scipy,kalvdans/scipy,richardotis/scipy,woodscn/scipy,arokem/scipy,cpaulik/scipy,aarchiba/scipy,trankmichael/scipy,raoulbq/scipy,matthew-brett/scipy,mortada/scipy,jakevdp/scipy,niknow/scipy,ilayn/scipy,aeklant/scipy,pnedunuri/scipy,matthewalbani/scipy,bkendzior/scipy,WarrenWeckesser/scipy,gfyoung/scipy,maniteja123/scipy,WillieMaddox/scipy,sauliusl/scipy,FRidh/scipy,hainm/scipy,e-q/scipy,mortonjt/scipy,behzadnouri/scipy,vanpact/scipy,ChanderG/scipy,petebachant/scipy,mortonjt/scipy,woodscn/scipy,maniteja123/scipy,mtrbean/scipy,zxsted/scipy,zxsted/scipy,raoulbq/scipy,dominicelse/scipy,jseabold/scipy,WarrenWeckesser/scipy,ortylp/scipy,jamestwebber/scipy,ales-erjavec/scipy,fernand/scipy,apbard/scipy,mtrbean/scipy,andim/scipy,mortonjt/scipy,kalvdans/scipy,mortonjt/scipy,gdooper/scipy,woodscn/scipy,vigna/scipy,ilayn/scipy,rmcgibbo/scipy,hainm/scipy,fredrikw/scipy,surhudm/scipy,pnedunuri/scipy,pbrod/scipy,juliantaylor/scipy,newemailjdm/scipy,ales-erjavec/scipy,jonycgn/scipy,newemailjdm/scipy,Shaswat27/scipy,ndchorley/scipy,mikebenfield/scipy,petebachant/scipy,sargas/scipy,teoliphant/scipy,jjhelmus/scipy,mdhaber/scipy,nmayorov/scipy,argriffing/scipy,gef756/scipy,pizzathief/scipy,sauliusl/scipy,vberaudi/scipy,rgommers/scipy,woodscn/scipy,gfyoung/scipy,vhaasteren/scipy,ales-erjavec/scipy,e-q/scipy,matthew-brett/scipy,endolith/scipy,felipebetancur/scipy,nonhermitian/scipy,arokem/scipy,Newman101/scipy,jonycgn/scipy,haudren/scipy,Shaswat27/scipy,lukauskas/scipy,rmcgibbo/scipy,pschella/scipy,anntzer/scipy,giorgiop/scipy,Srisai85/scipy,mdhaber/scipy,aarchiba/scipy,jsilter/scipy,sonnyhu/scipy,aman-iitj/scipy,chatcannon/scipy,petebachant/scipy,nonhermitian/scipy,e-q/scipy,perimosocordiae/scipy,jakevdp/scipy,vhaasteren/scipy,fernand/scipy,grlee77/scipy,mdhaber/scipy,gdooper/scipy,behzadnouri/scipy,grlee77/scipy,vanpact/scipy,jseabold/scipy,scipy/scipy,haudren/scipy,ortylp/scipy,maniteja123/scipy,maciejkula/scipy,argriffing/scipy,behzadnouri/scipy,mdhaber/scipy,minhlongdo/scipy,richardotis/scipy,gef756/scipy,kalvdans/scipy,teoliphant/scipy,newemailjdm/scipy,jakevdp/scipy,arokem/scipy,ilayn/scipy,mortada/scipy,mortada/scipy,josephcslater/scipy,larsmans/scipy,futurulus/scipy,endolith/scipy,sriki18/scipy,mgaitan/scipy,tylerjereddy/scipy,Srisai85/scipy,andim/scipy,gfyoung/scipy,Srisai85/scipy,matthewalbani/scipy,maciejkula/scipy,gertingold/scipy,befelix/scipy,jamestwebber/scipy,Newman101/scipy,maniteja123/scipy,efiring/scipy,pnedunuri/scipy,piyush0609/scipy,haudren/scipy,pschella/scipy,anielsen001/scipy,WillieMaddox/scipy,jsilter/scipy,befelix/scipy,trankmichael/scipy,aman-iitj/scipy,pizzathief/scipy,pschella/scipy,apbard/scipy,Dapid/scipy,anielsen001/scipy,vhaasteren/scipy,hainm/scipy,raoulbq/scipy,sonnyhu/scipy,gdooper/scipy,apbard/scipy,FRidh/scipy,minhlongdo/scipy,jakevdp/scipy,gfyoung/scipy,haudren/scipy,richardotis/scipy,jseabold/scipy,gertingold/scipy,anntzer/scipy,mingwpy/scipy,nvoron23/scipy,chatcannon/scipy,pyramania/scipy,teoliphant/sc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