Allow selector parser to specify pseudo-element which can be used with single-colon syntax.
Allow selector parser to specify pseudo-element which can be used with single-colon syntax.

CJ8664/servo,mattnenterprise/servo,emilio/servo,eddyb/servo,anthgur/servo,mbrubeck/servo,cbrewster/servo,thiagopnts/servo,szeged/servo,jimberlage/servo,emilio/servo,KiChjang/servo,splav/servo,peterjoel/servo,CJ8664/servo,mbrubeck/servo,pyfisch/servo,larsbergstrom/servo,mattnenterprise/servo,mbrubeck/servo,fiji-flo/servo,SimonSapin/servo,pyfisch/servo,DominoTree/servo,splav/servo,KiChjang/servo,emilio/servo,peterjoel/servo,szeged/servo,SimonSapin/servo,paulrouget/servo,dati91/servo,peterjoel/servo,saneyuki/servo,saneyuki/servo,jimberlage/servo,mattnenterprise/servo,cbrewster/servo,upsuper/servo,dati91/servo,cbrewster/servo,larsbergstrom/servo,canaltinova/servo,DominoTree/servo,nnethercote/servo,szeged/servo,rnestler/servo,KiChjang/servo,mattnenterprise/servo,avadacatavra/servo,KiChjang/servo,thiagopnts/servo,cbrewster/servo,notriddle/servo,rnestler/servo,DominoTree/servo,emilio/servo,paulrouget/servo,szeged/servo,notriddle/servo,SimonSapin/servo,SimonSapin/servo,thiagopnts/servo,notriddle/servo,peterjoel/servo,paulrouget/servo,dati91/servo,avadacatavra/servo,szeged/servo,ConnorGBrewster/servo,rnestler/servo,sadmansk/servo,upsuper/servo,dsandeephegde/servo,nnethercote/servo,thiagopnts/servo,anthgur/servo,splav/servo,anthgur/servo,saneyuki/servo,anthgur/servo,rnestler/servo,szeged/servo,szeged/servo,saneyuki/servo,splav/servo,SimonSapin/servo,DominoTree/servo,pyfisch/servo,SimonSapin/servo,nnethercote/servo,fiji-flo/servo,pyfisch/servo,szeged/servo,mbrubeck/servo,CJ8664/servo,eddyb/servo,rnestler/servo,ConnorGBrewster/servo,mbrubeck/servo,DominoTree/servo,larsbergstrom/servo,dsandeephegde/servo,mbrubeck/servo,KiChjang/servo,emilio/servo,larsbergstrom/servo,szeged/servo,mattnenterprise/servo,nnethercote/servo,peterjoel/servo,canaltinova/servo,CJ8664/servo,peterjoel/servo,upsuper/servo,splav/servo,eddyb/servo,SimonSapin/servo,pyfisch/servo,dsandeephegde/servo,ConnorGBrewster/servo,dati91/servo,saneyuki/servo,larsbergstrom/servo,avadacatavra/servo,eddyb/servo,nnethercote/servo,sadmansk/servo,mattnenterprise/servo,peterjoel/servo,saneyuki/servo,larsbergstrom/servo,paulrouget/servo,larsbergstrom/servo,saneyuki/servo,sadmansk/servo,canaltinova/servo,ConnorGBrewster/servo,emilio/servo,sadmansk/servo,DominoTree/servo,dsandeephegde/servo,szeged/servo,cbrewster/servo,mbrubeck/servo,canaltinova/servo,upsuper/servo,upsuper/servo,ConnorGBrewster/servo,CJ8664/servo,sadmansk/servo,KiChjang/servo,paulrouget/servo,eddyb/servo,larsbergstrom/servo,KiChjang/servo,ConnorGBrewster/servo,sadmansk/servo,cbrewster/servo,canaltinova/servo,pyfisch/servo,anthgur/servo,saneyuki/servo,eddyb/servo,dati91/servo,jimberlage/servo,notriddle/servo,paulrouget/servo,sadmansk/servo,rnestler/servo,dsandeephegde/servo,notriddle/servo,saneyuki/servo,canaltinova/servo,dati91/servo,sadmansk/servo,CJ8664/servo,anthgur/servo,KiChjang/servo,peterjoel/servo,upsuper/servo,paulrouget/servo,thiagopnts/servo,avadacatavra/servo,avadacatavra/servo,canaltinova/servo,KiChjang/servo,pyfisch/servo,eddyb/servo,dati91/servo,avadacatavra/servo,anthgur/servo,paulrouget/servo,jimberlage/servo,fiji-flo/servo,avadacatavra/servo,mattnenterprise/servo,larsbergstrom/servo,notriddle/servo,splav/servo,saneyuki/servo,pyfisch/servo,SimonSapin/servo,rnestler/servo,cbrewster/servo,fiji-flo/servo,DominoTree/servo,fiji-flo/servo,CJ8664/servo,DominoTree/servo,emilio/servo,emilio/servo,larsbergstrom/servo,notriddle/servo,dati91/servo,nnethercote/servo,upsuper/servo,pyfisch/servo,jimberlage/servo,CJ8664/servo,nnethercote/servo,pyfisch/servo,nnethercote/servo,emilio/servo,eddyb/servo,canaltinova/servo,splav/servo,anthgur/servo,jimberlage/servo,splav/servo,peterjoel/servo,fiji-flo/servo,jimberlage/servo,dsandeephegde/servo,DominoTree/servo,jimberlage/servo,thiagopnts/servo,thiagopnts/servo,KiChjang/servo,paulrouget/servo,paulrouget/servo,jimberlage/servo,nnethercote/servo,nnethercote/servo,DominoTree/servo,splav/servo,peterjoel/servo,cbrewster/servo,rnestler/servo,fiji-flo/servo,notriddle/servo,ConnorGBrewster/servo,thiagopnts/servo,mattnenterprise/servo,upsuper/servo,ConnorGBrewster/servo,dsandeephegde/servo,splav/servo,avadacatavra/servo,dsandeephegde/servo,mbrubeck/servo,emilio/servo,notriddle/servo,fiji-flo/servo,notriddle/servo