Partially revert commit a64dc0405064d68c7b7cd0f0fc8ea60086cbcd21.
Partially revert commit a64dc0405064d68c7b7cd0f0fc8ea60086cbcd21.

Removing the conditional was too liberal as now attr() would even work
on plain javascript objects. Keeping a check to make sure it is at least
a DOM Node is appropriate. Using nodeName as in the commit which introduced
the nodeType === 1 check seems plausible.

ilyakharlamov/jquery-xul,praveen9102/Shazam,praveen9102/Shazam,fat/jquery,chitranshi/jquery,roytoo/jquery,RubyLouvre/jquery,Karyotyper/jquery,quiaro/request-agent,demetr84/Jquery,scottjehl/jquery,jquery/jquery,gnarf/jquery,eburgos/jquery,rwaldron/jquery,npmcomponent/component-jquery,jquery/jquery,eburgos/jquery,isaacs/jquery,eburgos/jquery,hoorayimhelping/jquery,diracdeltas/jquery,chitranshi/jquery,npmcomponent/component-jquery,ilyakharlamov/jquery-xul,sancao2/jquery,fat/jquery,sancao2/jquery,Karyotyper/jquery,rwaldron/jquery,scottjehl/jquery,roytoo/jquery,RubyLouvre/jquery,jquery/jquery,jcutrell/jquery,kpozin/jquery-nodom,kpozin/jquery-nodom,jcutrell/jquery,dtjm/jquery,diracdeltas/jquery,diracdeltas/jquery,demetr84/Jquery,sancao2/jquery,dtjm/jquery,hoorayimhelping/jquery,Karyotyper/jquery,roytoo/jquery,isaacs/jquery,gnarf/jquery