fix error messages wrt what defines plural
fix error messages wrt what defines plural

Conflicts:
	sympy/core/function.py

souravsingh/sympy,kaushik94/sympy,hargup/sympy,MridulS/sympy,kevalds51/sympy,kaichogami/sympy,abloomston/sympy,aktech/sympy,rahuldan/sympy,grevutiu-gabriel/sympy,AkademieOlympia/sympy,meghana1995/sympy,saurabhjn76/sympy,ChristinaZografou/sympy,beni55/sympy,MechCoder/sympy,shipci/sympy,diofant/diofant,kaichogami/sympy,vipulroxx/sympy,debugger22/sympy,maniteja123/sympy,cswiercz/sympy,lindsayad/sympy,toolforger/sympy,sunny94/temp,kumarkrishna/sympy,sahilshekhawat/sympy,saurabhjn76/sympy,jerli/sympy,sunny94/temp,yukoba/sympy,sahilshekhawat/sympy,Vishluck/sympy,Sumith1896/sympy,iamutkarshtiwari/sympy,Arafatk/sympy,cccfran/sympy,atsao72/sympy,pandeyadarsh/sympy,Titan-C/sympy,kaushik94/sympy,jaimahajan1997/sympy,Shaswat27/sympy,yashsharan/sympy,Davidjohnwilson/sympy,jbbskinny/sympy,yashsharan/sympy,emon10005/sympy,kaushik94/sympy,toolforger/sympy,hargup/sympy,pbrady/sympy,Gadal/sympy,ahhda/sympy,kumarkrishna/sympy,chaffra/sympy,souravsingh/sympy,pandeyadarsh/sympy,lindsayad/sympy,Sumith1896/sympy,jamesblunt/sympy,ahhda/sympy,cswiercz/sympy,sampadsaha5/sympy,dqnykamp/sympy,Designist/sympy,chaffra/sympy,maniteja123/sympy,Titan-C/sympy,chaffra/sympy,ga7g08/sympy,Designist/sympy,beni55/sympy,Davidjohnwilson/sympy,farhaanbukhsh/sympy,Arafatk/sympy,shikil/sympy,cccfran/sympy,abhiii5459/sympy,madan96/sympy,Shaswat27/sympy,Vishluck/sympy,yashsharan/sympy,pbrady/sympy,postvakje/sympy,sahmed95/sympy,ahhda/sympy,drufat/sympy,farhaanbukhsh/sympy,farhaanbukhsh/sympy,shikil/sympy,madan96/sympy,MechCoder/sympy,moble/sympy,meghana1995/sympy,vipulroxx/sympy,garvitr/sympy,wyom/sympy,cccfran/sympy,meghana1995/sympy,VaibhavAgarwalVA/sympy,iamutkarshtiwari/sympy,wyom/sympy,shipci/sympy,Curious72/sympy,moble/sympy,Mitchkoens/sympy,iamutkarshtiwari/sympy,atreyv/sympy,atsao72/sympy,atreyv/sympy,Mitchkoens/sympy,ChristinaZografou/sympy,jamesblunt/sympy,wanglongqi/sympy,saurabhjn76/sympy,cswiercz/sympy,asm666/sympy,atsao72/sympy,kevalds51/sympy,debugger22/sympy,mafiya69/sympy,sampadsaha5/sympy,mafiya69/sympy,Vishluck/sympy,VaibhavAgarwalVA/sympy,skidzo/sympy,AunShiLord/sympy,ga7g08/sympy,maniteja123/sympy,jbbskinny/sympy,Mitchkoens/sympy,liangjiaxing/sympy,dqnykamp/sympy,oliverlee/sympy,wanglongqi/sympy,MridulS/sympy,garvitr/sympy,Gadal/sympy,atreyv/sympy,skirpichev/omg,debugger22/sympy,emon10005/sympy,AkademieOlympia/sympy,kevalds51/sympy,liangjiaxing/sympy,toolforger/sympy,mcdaniel67/sympy,wanglongqi/sympy,pandeyadarsh/sympy,madan96/sympy,bukzor/sympy,Shaswat27/sympy,bukzor/sympy,AunShiLord/sympy,vipulroxx/sympy,jerli/sympy,dqnykamp/sympy,Arafatk/sympy,MridulS/sympy,Curious72/sympy,Titan-C/sympy,yukoba/sympy,bukzor/sympy,yukoba/sympy,kaichogami/sympy,skidzo/sympy,asm666/sympy,aktech/sympy,Gadal/sympy,jamesblunt/sympy,garvitr/sympy,rahuldan/sympy,moble/sympy,sahilshekhawat/sympy,wyom/sympy,mcdaniel67/sympy,postvakje/sympy,sahmed95/sympy,asm666/sympy,hargup/sympy,mafiya69/sympy,abloomston/sympy,mcdaniel67/sympy,AunShiLord/sympy,Designist/sympy,beni55/sympy,jbbskinny/sympy,shikil/sympy,souravsingh/sympy,skidzo/sympy,pbrady/sympy,abhiii5459/sympy,oliverlee/sympy,oliverlee/sympy,AkademieOlympia/sympy,sunny94/temp,emon10005/sympy,grevutiu-gabriel/sympy,aktech/sympy,sampadsaha5/sympy,jaimahajan1997/sympy,abhiii5459/sympy,liangjiaxing/sympy,lindsayad/sympy,abloomston/sympy,jerli/sympy,shipci/sympy,drufat/sympy,MechCoder/sympy,rahuldan/sympy,ChristinaZografou/sympy,postvakje/sympy,Sumith1896/sympy,VaibhavAgarwalVA/sympy,drufat/sympy,Davidjohnwilson/sympy,Curious72/sympy,kumarkrishna/sympy,ga7g08/sympy,grevutiu-gabriel/sympy,sahmed95/sympy,jaimahajan1997/sympy