The comparison in airline#highlighter#exec() was there to prevent to
call out to too many :hi calls by making sure that the newly to be
defined highlighting group will be actually different from the current
existing one.
However, that did not work, as the returned old highlight
group did never match the newly to be created one, since it
intentionally left the cterm attributes out for the gui and the gui
attributes for the terminal.
Therefore, fix the comparasion and make it compare the actual values
that we have.
This should make vim-airline a bit faster (hopefully!)
560092a9ec