fugitive: mark fugitive like buffers with "[git]"

closes #1852

autoload/airline/extensions/fugitiveline.vim

@@ -8,7 +8,8 @@ if !airline#util#has_fugitive()
 endif
 
 
-if exists("+autochdir") && &autochdir == 1
+let s:has_autochdir = exists("+autochdir") && &autochdir
+if s:has_autochdir
   let s:fmod = ':p'
 else
   let s:fmod = ':.'
@@ -33,12 +34,12 @@ function! airline#extensions#fugitiveline#bufname()
   if empty(b:fugitive_name)
     return fnamemodify(bufname('%'), s:fmod)
   else
-    return fnamemodify(b:fugitive_name, s:fmod)
+    return fnamemodify(b:fugitive_name, s:fmod). " [git]"
   endif
 endfunction
 
 function! airline#extensions#fugitiveline#init(ext)
-  if exists("+autochdir") && &autochdir == 1
+  if s:has_autochdir
     " if 'acd' is set, vim-airline uses the path section, so we need to redefine this here as well
     call airline#parts#define_raw('path', '%<%{airline#extensions#fugitiveline#bufname()}%m')
   else

doc/airline.txt

@@ -599,6 +599,9 @@ It is deactivated by default if |airline-bufferline| is activated.
 * enable/disable bufferline integration >
   let g:airline#extensions#fugitiveline#enabled = 1
 <
+If enabled, the buffer that comes from fugitive, will have added a trailing
+"[git]" to be able do distinguish between fugitive and non-fugitive buffers.
+
 -------------------------------------                     *airline-grepper*
 vim-grepper <https://github.com/mhinz/vim-grepper>