Fix matching flags not being forwarded to regex_search
Fix matching flags not being forwarded to regex_search

Still does not fully fix #921

flavius/kakoune,danr/kakoune,lenormf/kakoune,lenormf/kakoune,alexherbo2/kakoune,jkonecny12/kakoune,ekie/kakoune,mawww/kakoune,casimir/kakoune,Somasis/kakoune,jjthrash/kakoune,jjthrash/kakoune,danr/kakoune,casimir/kakoune,Somasis/kakoune,mawww/kakoune,flavius/kakoune,casimir/kakoune,danr/kakoune,Somasis/kakoune,alexherbo2/kakoune,jjthrash/kakoune,danr/kakoune,flavius/kakoune,lenormf/kakoune,flavius/kakoune,jkonecny12/kakoune,ekie/kakoune,jkonecny12/kakoune,casimir/kakoune,occivink/kakoune,ekie/kakoune,occivink/kakoune,jkonecny12/kakoune,mawww/kakoune,occivink/kakoune,jjthrash/kakoune,occivink/kakoune,ekie/kakoune,lenormf/kakoune,mawww/kakoune,alexherbo2/kakoune,alexherbo2/kakoune,Somasis/kakoune