* It is more performant given now we process all the diff file instead
  of processing line by line.
* Multiline comments are highlighted correctly.

write_ was renamed to create_
modify_  was renamed to update_

So now in update action we have next code

def create
  can?(current_user, :create_issue, @issue)
end

def update
  can?(current_user, :update_issue, @issue)
end
Signed-off-by: NDmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Closes https://github.com/gitlabhq/gitlabhq/issues/9283

Signed-off-by: NDmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Also now removed lines relating to unused comments feature

TODO: fix comment forms to respect left and right columns