imageset improvments:
imageset improvments:

    1) canonicalize transformation from the input
       to be Lambda
    2) if _eval_imageset wasn't able to compute
       image - we return an unevaluated ImageSet object

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