Implement is_commutative for ExprCondPair.
Implement is_commutative for ExprCondPair.

For an ExprCondPair to be commutative, the Expr must be commutative.
There is then no need to override the is_commutative property for
Piecewise, as the one inherited from Function does the right thing.

liangjiaxing/sympy,yukoba/sympy,ga7g08/sympy,pbrady/sympy,abhiii5459/sympy,cswiercz/sympy,kaichogami/sympy,saurabhjn76/sympy,meghana1995/sympy,pbrady/sympy,atreyv/sympy,skidzo/sympy,rahuldan/sympy,dqnykamp/sympy,cccfran/sympy,beni55/sympy,wyom/sympy,Arafatk/sympy,lindsayad/sympy,skirpichev/omg,sahmed95/sympy,ChristinaZografou/sympy,jerli/sympy,vipulroxx/sympy,shipci/sympy,sunny94/temp,abhiii5459/sympy,Designist/sympy,souravsingh/sympy,postvakje/sympy,chaffra/sympy,abloomston/sympy,saurabhjn76/sympy,toolforger/sympy,jbbskinny/sympy,cswiercz/sympy,Titan-C/sympy,ga7g08/sympy,mafiya69/sympy,Mitchkoens/sympy,maniteja123/sympy,kaushik94/sympy,chaffra/sympy,debugger22/sympy,aktech/sympy,pbrady/sympy,Davidjohnwilson/sympy,meghana1995/sympy,mafiya69/sympy,kumarkrishna/sympy,jamesblunt/sympy,oliverlee/sympy,yashsharan/sympy,yukoba/sympy,jaimahajan1997/sympy,abloomston/sympy,hrashk/sympy,hargup/sympy,flacjacket/sympy,atsao72/sympy,vipulroxx/sympy,shikil/sympy,bukzor/sympy,pandeyadarsh/sympy,iamutkarshtiwari/sympy,Davidjohnwilson/sympy,wanglongqi/sympy,AkademieOlympia/sympy,Davidjohnwilson/sympy,shikil/sympy,dqnykamp/sympy,AunShiLord/sympy,wyom/sympy,sahilshekhawat/sympy,rahuldan/sympy,yukoba/sympy,wyom/sympy,shikil/sympy,hrashk/sympy,Curious72/sympy,MechCoder/sympy,AunShiLord/sympy,bukzor/sympy,AkademieOlympia/sympy,Curious72/sympy,emon10005/sympy,jaimahajan1997/sympy,abloomston/sympy,dqnykamp/sympy,kmacinnis/sympy,ahhda/sympy,aktech/sympy,skidzo/sympy,chaffra/sympy,Shaswat27/sympy,sampadsaha5/sympy,emon10005/sympy,mcdaniel67/sympy,mcdaniel67/sympy,kmacinnis/sympy,asm666/sympy,atsao72/sympy,kaichogami/sympy,pandeyadarsh/sympy,ahhda/sympy,garvitr/sympy,Vishluck/sympy,ChristinaZografou/sympy,sahilshekhawat/sympy,Mitchkoens/sympy,garvitr/sympy,cccfran/sympy,drufat/sympy,MridulS/sympy,jerli/sympy,asm666/sympy,iamutkarshtiwari/sympy,AunShiLord/sympy,VaibhavAgarwalVA/sympy,souravsingh/sympy,sampadsaha5/sympy,madan96/sympy,jerli/sympy,shipci/sympy,Titan-C/sympy,wanglongqi/sympy,sampadsaha5/sympy,jaimahajan1997/sympy,rahuldan/sympy,kumarkrishna/sympy,drufat/sympy,moble/sympy,hrashk/sympy,Vishluck/sympy,toolforger/sympy,beni55/sympy,amitjamadagni/sympy,Sumith1896/sympy,debugger22/sympy,souravsingh/sympy,sahmed95/sympy,kevalds51/sympy,Mitchkoens/sympy,hargup/sympy,AkademieOlympia/sympy,postvakje/sympy,kaushik94/sympy,ga7g08/sympy,atreyv/sympy,garvitr/sympy,Vishluck/sympy,lidavidm/sympy,hargup/sympy,amitjamadagni/sympy,moble/sympy,jamesblunt/sympy,shipci/sympy,cccfran/sympy,jbbskinny/sympy,liangjiaxing/sympy,skidzo/sympy,Gadal/sympy,bukzor/sympy,jbbskinny/sympy,iamutkarshtiwari/sympy,Designist/sympy,sahmed95/sympy,postvakje/sympy,Titan-C/sympy,vipulroxx/sympy,grevutiu-gabriel/sympy,Arafatk/sympy,Sumith1896/sympy,lidavidm/sympy,maniteja123/sympy,farhaanbukhsh/sympy,oliverlee/sympy,Gadal/sympy,kaichogami/sympy,saurabhjn76/sympy,jamesblunt/sympy,cswiercz/sympy,yashsharan/sympy,Shaswat27/sympy,farhaanbukhsh/sympy,atreyv/sympy,diofant/diofant,asm666/sympy,sahilshekhawat/sympy,MechCoder/sympy,Designist/sympy,moble/sympy,Sumith1896/sympy,beni55/sympy,ChristinaZografou/sympy,debugger22/sympy,sunny94/temp,Shaswat27/sympy,lindsayad/sympy,abhiii5459/sympy,mafiya69/sympy,madan96/sympy,kmacinnis/sympy,liangjiaxing/sympy,Curious72/sympy,Gadal/sympy,MridulS/sympy,mcdaniel67/sympy,kevalds51/sympy,kevalds51/sympy,VaibhavAgarwalVA/sympy,emon10005/sympy,MechCoder/sympy,oliverlee/sympy,pandeyadarsh/sympy,kumarkrishna/sympy,lidavidm/sympy,meghana1995/sympy,sunny94/temp,lindsayad/sympy,grevutiu-gabriel/sympy,Arafatk/sympy,drufat/sympy,atsao72/sympy,wanglongqi/sympy,yashsharan/sympy,VaibhavAgarwalVA/sympy,aktech/sympy,grevutiu-gabriel/sympy,ahhda/sympy,farhaanbukhsh/sympy,srjoglekar246/sympy,MridulS/sympy,kaushik94/sympy,maniteja123/sympy,madan96/sympy,toolforger/sympy