implement funcref list again, this time with a global function as this affects older versions of vim

autoload/airline.vim

@@ -68,7 +68,9 @@ function! s:apply_window_overrides()
     let w:airline_section_c = bufname(winbufnr(winnr()))
   endif
 
-  call airline#extensions#apply_window_overrides()
+  for FuncRef in g:airline_window_override_funcrefs
+    call FuncRef()
+  endfor
 endfunction
 
 function! airline#update_externals()

autoload/airline/extensions.vim

@@ -1,23 +1,5 @@
 let s:sections = ['a','b','c','gutter','x','y','z']
 
-function! airline#extensions#load()
-  let g:unite_force_overwrite_statusline = 0
-
-  if exists('g:loaded_ctrlp') && g:loaded_ctrlp
-    call airline#extensions#ctrlp#load_ctrlp_hi()
-    let g:ctrlp_status_func = {
-          \ 'main': 'airline#extensions#ctrlp#ctrlp_airline',
-          \ 'prog': 'airline#extensions#ctrlp#ctrlp_airline_status',
-          \ }
-  endif
-endfunction
-
-function! s:empty_sections()
-  for section in s:sections
-    let w:airline_section_{section} = ''
-  endfor
-endfunction
-
 function! s:override_left_only(section1, section2)
   let w:airline_section_a = a:section1
   let w:airline_section_b = a:section2
@@ -49,3 +31,18 @@ function! airline#extensions#apply_window_overrides()
     call s:override_left_only('MiniBufExplorer', '')
   endif
 endfunction
+
+function! airline#extensions#load()
+  let g:unite_force_overwrite_statusline = 0
+
+  if exists('g:loaded_ctrlp') && g:loaded_ctrlp
+    call airline#extensions#ctrlp#load_ctrlp_hi()
+    let g:ctrlp_status_func = {
+          \ 'main': 'airline#extensions#ctrlp#ctrlp_airline',
+          \ 'prog': 'airline#extensions#ctrlp#ctrlp_airline_status',
+          \ }
+  endif
+
+  call add(g:airline_window_override_funcrefs, function('airline#extensions#apply_window_overrides'))
+endfunction
+

plugin/airline.vim

@@ -50,6 +50,8 @@ function! s:init()
   endif
 endfunction
 
+let g:airline_window_override_funcrefs = []
+
 augroup airline
   au!
   autocmd ColorScheme * call airline#highlight(['normal'])