add whitespace toggle command

autoload/airline/extensions.vim

@@ -137,7 +137,7 @@ function! airline#extensions#load()
   endif
 
   if g:airline_detect_whitespace
-    call airline#extensions#whitespace#init(s:ext)
+    call airline#extensions#whitespace#init()
   endif
 
   call airline#exec_funcrefs(g:airline_statusline_funcrefs, 0)

autoload/airline/extensions/whitespace.vim

@@ -4,7 +4,7 @@
 " http://got-ravings.blogspot.com/2008/10/vim-pr0n-statusline-whitespace-flags.html
 
 function! airline#extensions#whitespace#check()
-  if &readonly
+  if &readonly || !g:airline_detect_whitespace
     return ''
   endif
 
@@ -37,8 +37,21 @@ function! airline#extensions#whitespace#apply()
   endif
 endfunction
 
-function! airline#extensions#whitespace#init(ext)
+function! airline#extensions#whitespace#toggle()
-  call a:ext.add_statusline_funcref(function('airline#extensions#whitespace#apply'))
+  let g:airline_detect_whitespace = !g:airline_detect_whitespace
+  if g:airline_detect_whitespace
+    call airline#extensions#whitespace#init()
+  else
+    autocmd! airline_whitespace CursorHold,BufWritePost
+  endif
+endfunction
+
+let s:initialized = 0
+function! airline#extensions#whitespace#init()
+  if !s:initialized
+    let s:initialized = 1
+    call add(g:airline_statusline_funcrefs, function('airline#extensions#whitespace#apply'))
+  endif
 
   augroup airline_whitespace
     autocmd!

doc/airline.txt

@@ -120,6 +120,9 @@ COMMANDS                                                  *airline-commands*
 :AirlineTheme {theme-name}                                   *:AirlineTheme*
   Displays or changes the current theme.
 
+:AirlineToggleWhitespace                          *:AirlineToggleWhitespace*
+  Toggles whitespace detection.
+
 ==============================================================================
 CUSTOMIZATION                                        *airline-customization*
 

plugin/airline.vim

@@ -80,6 +80,7 @@ function! s:airline_theme(...)
   endif
 endfunction
 command! -nargs=? -complete=customlist,<sid>get_airline_themes AirlineTheme call <sid>airline_theme(<f-args>)
+command! AirlineToggleWhitespace call airline#extensions#whitespace#toggle()
 
 augroup airline
   autocmd!