Set qflist/loclist window title properly ... (#588)

* Update list.vim

Set qflist/loclist window title properly ...

* Update list.vim

1. Remove redundant code.
2. Get absolute path from 'a:buffer'.

* Set the list window titles appropriately for each version of Vim, and add tests

test/test_list_titles.vader

@@ -0,0 +1,63 @@
+Before:
+  Save g:ale_set_loclist
+  Save g:ale_set_quickfix
+
+  let g:ale_set_loclist = 0
+  let g:ale_set_quickfix = 0
+
+  silent! cd /testplugin/test
+
+After:
+  Restore
+
+  call setloclist(0, [])
+  call setqflist([])
+
+Execute(The loclist titles should be set appropriately):
+  silent noautocmd file foo
+
+  let g:ale_set_loclist = 1
+
+  call ale#list#SetLists(bufnr(''), [
+  \ {'bufnr': bufnr(''), 'lnum': 5, 'col': 5, 'text': 'x', 'type': 'E'},
+  \])
+
+  AssertEqual [{
+  \ 'lnum': 5,
+  \ 'bufnr': bufnr(''),
+  \ 'col': 5,
+  \ 'text': 'x',
+  \ 'valid': 1,
+  \ 'vcol': 0,
+  \ 'nr': 0,
+  \ 'type': 'E',
+  \ 'pattern': '',
+  \}], getloclist(0)
+
+  if !has('nvim')
+    AssertEqual {'title': getcwd() . '/foo'}, getloclist(0, {'title': ''})
+  endif
+
+Execute(The quickfix titles should be set appropriately):
+  silent noautocmd file foo
+
+  let g:ale_set_quickfix = 1
+
+  call ale#list#SetLists(bufnr(''), [
+  \ {'bufnr': bufnr(''), 'lnum': 5, 'col': 5, 'text': 'x', 'type': 'E'},
+  \])
+  AssertEqual [{
+  \ 'lnum': 5,
+  \ 'bufnr': bufnr(''),
+  \ 'col': 5,
+  \ 'text': 'x',
+  \ 'valid': 1,
+  \ 'vcol': 0,
+  \ 'nr': 0,
+  \ 'type': 'E',
+  \ 'pattern': '',
+  \}], getqflist()
+
+  if !has('nvim')
+    AssertEqual {'title': getcwd() . '/foo'}, getqflist({'title': ''})
+  endif