Do not tag BufferIterator as random access
Do not tag BufferIterator as random access

Boost regex considers that random access means fast distance
computation, which is not the case for BufferIterator where
Buffer::distance is O(num lines between them) which can get
big on large files.

Fixes #462

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