shorten tagbar extension on short windows

autoload/airline/util.vim

@@ -6,9 +6,15 @@ scriptencoding utf-8
 call airline#init#bootstrap()
 let s:spc = g:airline_symbols.space
 
-function! airline#util#shorten(text, winwidth, minwidth)
+function! airline#util#shorten(text, winwidth, minwidth, ...)
   if winwidth(0) < a:winwidth && len(split(a:text, '\zs')) > a:minwidth
+    if get(a:000, 0, 0)
+      " shorten from tail
+      return '…'.matchstr(a:text, '.\{'.a:minwidth.'}$')
+    else
+      " shorten from beginning of string
       return matchstr(a:text, '^.\{'.a:minwidth.'}').'…'
+    endif
   else
     return a:text
   endif