1) Make sure airline_error and airline_warning highlighting are
different, so that the correct separator will be drawn. This
fixes#982.
2) allow to deactivate %(%) to workaround a vim bug, that may cause
leaking of colors from one section to the next and adding additional
spaces. This needs to be fixed upstream:
https://groups.google.com/d/msg/vim_dev/sb1jmVirXPU/mPhvDnZ-CwAJ
Possibly, also related to neovim/neovim#4147
Use `:let airline#extensions#default#section_use_groupitems = 0`
to disable grouping of statusline items
f57c5daf66