fix loc list auto close. see vim-syntastic#123

 - changed BufLeave to BufWinLeave otherwise it would close when
   jumping to loc list.
 - extracted method that auto close/open location list based on
   errors/settings and make sure it reopens loclist when buffer is
   displayed (BufWinEnter) if needed.

plugin/syntastic.vim

@@ -89,8 +89,9 @@ augroup syntastic
         autocmd cursormoved * call s:EchoCurrentError()
     endif
 
-    autocmd BufReadPost,BufWritePost,BufEnter * call s:UpdateErrors(1)
-    autocmd BufUnload,BufLeave * lclose
+    autocmd BufReadPost,BufWritePost * call s:UpdateErrors(1)
+    autocmd BufWinEnter * if empty(&bt) | call s:AutoToggleLocList() | endif
+    autocmd BufUnload,BufWinLeave * lclose
 augroup END
 
 
@@ -112,6 +113,11 @@ function! s:UpdateErrors(auto_invoked)
         call s:RefreshSigns()
     endif
 
+    call s:AutoToggleLocList()
+
+endfunction
+
+function s:AutoToggleLocList()
     if s:BufHasErrorsOrWarningsToDisplay()
         call setloclist(0, b:syntastic_loclist)
         if g:syntastic_auto_jump