#653 Collect items for quickfix from all buffers, and de-duplicate them. Set filename items in quickfix and loclist.

test/test_setting_loclist_from_another_buffer.vader

@@ -1,7 +1,11 @@
 Before:
   Save g:ale_buffer_info
 
-  let g:ale_buffer_info = {}
+  let g:ale_buffer_info = {
+  \ bufnr(''): {
+  \   'loclist': [{'bufnr': bufnr(''), 'lnum': 4, 'col': 1, 'text': 'foo'}]
+  \ },
+  \}
 
   let g:original_buffer = bufnr('%')
   noautocmd new
@@ -12,7 +16,10 @@ After:
   unlet! g:original_buffer
 
 Execute(Errors should be set in the loclist for the original buffer, not the new one):
-  call ale#list#SetLists(g:original_buffer, [{'lnum': 4, 'text': 'foo'}])
+  call ale#list#SetLists(
+  \ g:original_buffer,
+  \ g:ale_buffer_info[(g:original_buffer)].loclist,
+  \ )
 
   AssertEqual [], getloclist(0)
   AssertEqual 1, len(getloclist(bufwinid(g:original_buffer)))