introduce gutter section so the entire statusline can be overwritten

README.md

@@ -47,7 +47,7 @@ this plugin follows the standard runtime path structure, and as such it can be i
 *  there is a pause when leaving insert mode
   *  you need to set `ttimeoutlen` to a low number; 50 is recommended
 *  you don't see any colors
-  *  the value of `t_Co` is likely misconfigured.  please see this [article][n].
+  *  all of the themes use a 256 terminal color palette.  it's likely that the value of `t_Co` is misconfigured.  please see this [article][n] on how to configure your terminal.  pull requests for 8 and 16 color terminals are welcome.
 *  you get the error `Unknown function: fugitive#head`
   *  you are probably using version 1.2, which is very old...download v2 from the [project page][d].
 *  airline doesn't appear until i create a new split
@@ -57,7 +57,7 @@ this plugin follows the standard runtime path structure, and as such it can be i
 
 # bugs
 
-if you encounter a bug, please reproduce it with this [minivimrc][g] repository i created and file an issue.
+if you encounter a bug, please reproduce it with this [minivimrc][g] repository i created and file an issue.  please provide your operating system and vim version/patch level (can be found with `:version`).  a reproducible gist would be hugely helpful.
 
 # screenshots
 

autoload/airline.vim

@@ -103,8 +103,9 @@ function! airline#update_statusline(active)
   let sl.=l:info_sep_color
   let sl.=a:active ? g:airline_left_sep : g:airline_left_alt_sep
   let sl.=a:active ? l:status_color.' '.s:get_section('c').' ' : ' '.bufname(winbufnr(winnr()))
-  let sl.='%#warningmsg#'.g:airline_externals_syntastic
-  let sl.=l:status_color."%<%=".l:file_flag_color."%{&ro ? g:airline_readonly_symbol : ''}".l:status_color
+  let sl.=g:airline_section_gutter != ''
+        \ ? g:airline_section_gutter
+        \ : '%#warningmsg#'.g:airline_externals_syntastic.l:status_color."%<%=".l:file_flag_color."%{&ro ? g:airline_readonly_symbol : ''}".l:status_color
   let sl.=' '.s:get_section('x').' '
   let sl.=l:info_sep_color
   let sl.=a:active ? g:airline_right_sep : g:airline_right_alt_sep

doc/airline.txt

@@ -112,12 +112,13 @@ with the usual statusline syntax.
 
 >
   " here are the the default values
-  let g:airline_section_a (the mode indicator)
-  let g:airline_section_b (the fugitive branch indicator)
-  let g:airline_section_c (bufferline or filename)
-  let g:airline_section_x (filetype)
-  let g:airline_section_y (fileencoding, fileformat)
-  let g:airline_section_z (percentage, line number, column number)
+  let g:airline_section_a      (the mode indicator)
+  let g:airline_section_b      (the fugitive branch indicator)
+  let g:airline_section_c      (bufferline or filename)
+  let g:airline_section_gutter (syntastic and readonly flag)
+  let g:airline_section_x      (filetype)
+  let g:airline_section_y      (fileencoding, fileformat)
+  let g:airline_section_z      (percentage, line number, column number)
 <
 
 ==============================================================================

plugin/airline.vim

@@ -41,6 +41,7 @@ function! s:init()
     call s:check_defined('g:airline_section_a', '%{g:airline_current_mode_text}')
     call s:check_defined('g:airline_section_b', '%{g:airline_externals_fugitive}')
     call s:check_defined('g:airline_section_c', g:airline_externals_bufferline)
+    call s:check_defined('g:airline_section_gutter', '')
     call s:check_defined('g:airline_section_x', "%{strlen(&filetype)>0?&filetype:''}")
     call s:check_defined('g:airline_section_y', "%{strlen(&fenc)>0?&fenc:''}%{strlen(&ff)>0?'['.&ff.']':''}")
     call s:check_defined('g:airline_section_z', '%3p%% '.g:airline_linecolumn_prefix.'%3l:%3c')