Print stderr output of LanguageTool command if it fails to help

diagnose why LanguageTool command line may fail.

plugin/LanguageTool.vim

@@ -2,8 +2,8 @@
 " Maintainer:   Dominique Pellé <[email protected]>
 " Screenshots:  http://dominique.pelle.free.fr/pic/LanguageToolVimPlugin_en.png
 "               http://dominique.pelle.free.fr/pic/LanguageToolVimPlugin_fr.png
-" Last Change:  2013/08/10
-" Version:      1.25
+" Last Change:  2013/10/24
+" Version:      1.27
 "
 " Long Description: {{{1
 "
@@ -230,6 +230,7 @@ function s:LanguageToolCheck(line1, line2) "{{{1
   " reading from stdin so we need to use a temporary file to get
   " correct results.
   let l:tmpfilename = tempname()
+  let l:tmperror    = tempname()
 
   let l:range = a:line1 . ',' . a:line2
   silent exe l:range . 'w!' . l:tmpfilename
@@ -240,16 +241,22 @@ function s:LanguageToolCheck(line1, line2) "{{{1
   \ . ' -d '    . s:languagetool_disable_rules
   \ . ' -l '    . s:languagetool_lang
   \ . ' --api ' . l:tmpfilename
+  \ . ' 2> '    . l:tmperror
 
   sil exe '%!' . l:languagetool_cmd
   call delete(l:tmpfilename)
 
   if v:shell_error
     echoerr 'Command [' . l:languagetool_cmd . '] failed with error: '
     \      . v:shell_error
+    if filereadable(l:tmperror)
+      echoerr string(readfile(l:tmperror))
+    endif
+    call delete(l:tmperror)
     call s:LanguageToolClear()
     return -1
   endif
+  call delete(l:tmperror)
 
   " Loop on all errors in XML output of LanguageTool and
   " collect information about all errors in list s:errors