rework basestring check in BytesQuery
rework basestring check in BytesQuery

This makes it possible for this query to work in both py2 and py3,
since strings are bytes in py2

shamangeorge/beets,MyTunesFreeMusic/privacy-policy,artemutin/beets,sampsyo/beets,shamangeorge/beets,jcoady9/beets,madmouser1/beets,Kraymer/beets,MyTunesFreeMusic/privacy-policy,jcoady9/beets,diego-plan9/beets,madmouser1/beets,Kraymer/beets,SusannaMaria/beets,diego-plan9/beets,ibmibmibm/beets,diego-plan9/beets,xsteadfastx/beets,xsteadfastx/beets,shamangeorge/beets,SusannaMaria/beets,mosesfistos1/beetbox,artemutin/beets,lengtche/beets,ibmibmibm/beets,madmouser1/beets,ibmibmibm/beets,MyTunesFreeMusic/privacy-policy,Kraymer/beets,artemutin/beets,mosesfistos1/beetbox,MyTunesFreeMusic/privacy-policy,SusannaMaria/beets,jcoady9/beets,sampsyo/beets,lengtche/beets,jackwilsdon/beets,sampsyo/beets,mosesfistos1/beetbox,pkess/beets,lengtche/beets,jackwilsdon/beets,jackwilsdon/beets,jackwilsdon/beets,beetbox/beets,lengtche/beets,beetbox/beets,Kraymer/beets,pkess/beets,pkess/beets,beetbox/beets,madmouser1/beets,artemutin/beets,mosesfistos1/beetbox,pkess/beets,xsteadfastx/beets,shamangeorge/beets,ibmibmibm/beets,diego-plan9/beets,SusannaMaria/beets,sampsyo/beets,beetbox/beets,jcoady9/beets,xsteadfastx/beets