Added _eval_rewrite_as_pow for both sin and cos
Added _eval_rewrite_as_pow for both sin and cos

These call _eval_rewrite_as_sqrt currently.  The sine
form converts to cosine first.

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