MinMaxBase will raise error if args are not Expr's
MinMaxBase will raise error if args are not Expr's

This also fix deprecation warnings like this:
>>> s = FiniteSet(FiniteSet(1, 2, 3))
>>> s
{{1, 2, 3}}
>>> len(s)
1
>>> s.powerset()
/usr/lib/python3.3/site-packages/sympy-0.7.5_git-py3.3.egg/sympy/functions/elementary/miscellaneous.py:334:
SymPyDeprecationWarning:

is_real has been deprecated since SymPy 0.7.6. Use is_subset(Reals)
instead. See https://github.com/sympy/sympy/issues/6212 for more info.

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