*: Move some dictionary functions to typval.h and use char*

Also fixes buffer reusage in setmatches() and complete().

test/functional/eval/string_spec.lua

@@ -7,7 +7,6 @@ local eval = helpers.eval
 local exc_exec = helpers.exc_exec
 local redir_exec = helpers.redir_exec
 local funcs = helpers.funcs
-local write_file = helpers.write_file
 local NIL = helpers.NIL
 local source = helpers.source
 local dedent = helpers.dedent
@@ -105,10 +104,8 @@ describe('string() function', function()
   end)
 
   describe('used to represent funcrefs', function()
-    local fname = 'Xtest-functional-eval-string_spec-fref-script.vim'
-
     before_each(function()
-      write_file(fname, [[
+      source([[
         function Test1()
         endfunction
 
@@ -120,11 +117,6 @@ describe('string() function', function()
 
         let g:Test2_f = function('s:Test2')
       ]])
-      command('source ' .. fname)
-    end)
-
-    after_each(function()
-      os.remove(fname)
     end)
 
     it('dumps references to built-in functions', function()