extract buffer name logic into a formatter.

hold off on deprecation warnings for now...

autoload/airline/extensions/tabline/formatters.vim

@@ -0,0 +1,29 @@
+" MIT License. Copyright (c) 2013 Bailey Ling.
+" vim: et ts=2 sts=2 sw=2
+
+let s:buf_nr_format = get(g:, 'airline#extensions#tabline#buffer_nr_format', '%s: ')
+let s:buf_nr_show = get(g:, 'airline#extensions#tabline#buffer_nr_show', 0)
+let s:buf_modified_symbol = g:airline_symbols.modified
+
+function! airline#extensions#tabline#formatters#default(bufnr)
+  let _ = ''
+
+  if s:buf_nr_show
+    let _ .= printf(s:buf_nr_format, a:bufnr)
+  endif
+
+  let name = bufname(a:bufnr)
+  let fmod = get(g:, 'airline#extensions#tabline#fnamemod', ':p:.')
+  if empty(name)
+    let _ .= '[No Name]'
+  else
+    let _ .= substitute(fnamemodify(name, fmod), '\w\zs.\{-}\ze\/', '', 'g')
+  endif
+
+  if getbufvar(a:bufnr, '&modified') == 1
+    let _ .= s:buf_modified_symbol
+  endif
+
+  return _
+endfunction
+