improve test script: avoid func_ref to script local function

test/test.vim

@@ -1,22 +1,18 @@
 let s:assert = themis#helper('assert')
 
-function! s:before()
-  filetype plugin indent on
-  setlocal filetype=haskell
-  setlocal formatoptions-=cro
-endfunction
-
-function! s:before_each()
-  % delete _
-  setlocal expandtab shiftwidth=2
-  let g:haskell_indent_disable_case = 0
-endfunction
-
 function! s:test(path)
   for path in filter(split(glob(a:path . '/*')), 'isdirectory(v:val)')
     let suite = themis#suite('Test for ' . matchstr(path, '\w*$'))
-    let suite.before = function('s:before')
-    let suite.before_each = function('s:before_each')
+    function! suite.before() abort
+      filetype plugin indent on
+      setlocal filetype=haskell
+      setlocal formatoptions-=cro
+    endfunction
+    function! suite.before_each() abort
+      % delete _
+      setlocal expandtab shiftwidth=2
+      let g:haskell_indent_disable_case = 0
+    endfunction
     for infile in split(glob(path . '/*.in.hs', 1), "\n")
       execute join([
             \ 'function! suite.' . matchstr(infile, '\w*\ze\.in\.hs$') . '()'