allow to use alternative seperators for inactive windows

closes #1236

autoload/airline.vim

@@ -146,6 +146,11 @@ function! airline#update_statusline_inactive(range)
     endif
     call setwinvar(nr, 'airline_active', 0)
     let context = { 'winnr': nr, 'active': 0, 'bufnr': winbufnr(nr) }
+    if get(g:, 'airline_inactive_alt_sep', 0)
+      call extend(context, {
+            \ 'left_sep': g:airline_left_alt_sep,
+            \ 'right_sep': g:airline_right_alt_sep }, 'keep')
+    endif
     call s:invoke_funcrefs(context, s:inactive_funcrefs)
   endfor
 endfunction

doc/airline.txt

@@ -142,6 +142,9 @@ values):
   only the filename of that buffer.  >
   let g:airline_inactive_collapse=1
 <
+* Use alternative seperators for the statusline of inactive windows >
+  let g:airline_inactive_alt_sep=1 
+<
 * themes are automatically selected based on the matching colorscheme. this
   can be overridden by defining a value. >
   let g:airline_theme='dark'