make 'callback' an optparse typed action
make 'callback' an optparse typed action

* this ensures metavars are shown with print_help

marcuskrahl/beets,drm00/beets,LordSputnik/beets,jackwilsdon/beets,ttsda/beets,randybias/beets,LordSputnik/beets,sadatay/beets,kelvinhammond/beets,madmouser1/beets,m-urban/beets,Wen777/beets,sadatay/beets,beetbox/beets,gabrielaraujof/beets,Freso/beets,Andypsamp/CODjunit,madmouser1/beets,gabrielaraujof/beets,beetbox/beets,asteven/beets,kelvinhammond/beets,bj-yinyan/beets,madmouser1/beets,arabenjamin/beets,sampsyo/beets,jcoady9/beets,Andypsamp/CODjunit,jackwilsdon/beets,moodboom/beets,xsteadfastx/beets,ibmibmibm/beets,moodboom/beets,shamangeorge/beets,mathstuf/beets,YetAnotherNerd/beets,imsparsh/beets,bj-yinyan/beets,swt30/beets,beetbox/beets,jcoady9/beets,shamangeorge/beets,artemutin/beets,parapente/beets,Andypsamp/CODfinalJUNIT,xsteadfastx/beets,Wen777/beets,andremiller/beets,MyTunesFreeMusic/privacy-policy,SusannaMaria/beets,pkess/beets,drm00/beets,pkess/beets,jmwatte/beets,shanemikel/beets,ttsda/beets,multikatt/beets,marcuskrahl/beets,marcuskrahl/beets,Freso/beets,jcoady9/beets,andremiller/beets,lightwang1/beets,diego-plan9/beets,MyTunesFreeMusic/privacy-policy,mosesfistos1/beetbox,drm00/beets,shanemikel/beets,arabenjamin/beets,SusannaMaria/beets,diego-plan9/beets,swt30/beets,ibmibmibm/beets,Kraymer/beets,tima/beets,drm00/beets,jackwilsdon/beets,ibmibmibm/beets,lightwang1/beets,Dishwishy/beets,Freso/beets,Kraymer/beets,dfc/beets,jmwatte/beets,ruippeixotog/beets,bj-yinyan/beets,asteven/beets,krig/beets,shanemikel/beets,lengtche/beets,kareemallen/beets,LordSputnik/beets,lightwang1/beets,randybias/beets,asteven/beets,PierreRust/beets,shanemikel/beets,parapente/beets,ruippeixotog/beets,MyTunesFreeMusic/privacy-policy,lengtche/beets,multikatt/beets,andremiller/beets,untitaker/beets,diego-plan9/beets,sadatay/beets,marcuskrahl/beets,Dishwishy/beets,imsparsh/beets,tima/beets,multikatt/beets,xsteadfastx/beets,kareemallen/beets,mathstuf/beets,parapente/beets,asteven/beets,untitaker/beets,bj-yinyan/beets,Freso/beets,YetAnotherNerd/beets,YetAnotherNerd/beets,artemutin/beets,Andypsamp/CODjunit,randybias/beets,sampsyo/beets,multikatt/beets,lengtche/beets,sampsyo/beets,swt30/beets,SusannaMaria/beets,mried/beets,ibmibmibm/beets,m-urban/beets,Andypsamp/CODfinalJUNIT,untitaker/beets,PierreRust/beets,imsparsh/beets,madmouser1/beets,pkess/beets,jcoady9/beets,untitaker/beets,swt30/beets,diego-plan9/beets,arabenjamin/beets,kelvinhammond/beets,kareemallen/beets,YetAnotherNerd/beets,Andypsamp/CODfinalJUNIT,Andypsamp/CODfinalJUNIT,LordSputnik/beets,dfc/beets,kareemallen/beets,ruippeixotog/beets,Wen777/beets,pkess/beets,mried/beets,ttsda/beets,tima/beets,ttsda/beets,mosesfistos1/beetbox,sampsyo/beets,Dishwishy/beets,parapente/beets,gabrielaraujof/beets,mosesfistos1/beetbox,krig/beets,lengtche/beets,Andypsamp/CODjunit,shamangeorge/beets,mried/beets,dfc/beets,dfc/beets,MyTunesFreeMusic/privacy-policy,moodboom/beets,mried/beets,artemutin/beets,jmwatte/beets,beetbox/beets,ruippeixotog/beets,xsteadfastx/beets,mathstuf/beets,PierreRust/beets,jackwilsdon/beets,Andypsamp/CODjunit,Kraymer/beets,mathstuf/beets,kelvinhammond/beets,moodboom/beets,m-urban/beets,mosesfistos1/beetbox,gabrielaraujof/beets,lightwang1/beets,SusannaMaria/beets,m-urban/beets,sadatay/beets,shamangeorge/beets,arabenjamin/beets,tima/beets,PierreRust/beets,artemutin/beets,krig/beets,jmwatte/beets,imsparsh/beets,randybias/beets,Andypsamp/CODfinalJUNIT,Kraymer/beets,Dishwishy/beets