Fix #434 - Use runtime to load syntax file during ft-based ODL

A plugin may have 'after/syntax/foo.vim' without 'syntax/foo.vim'.

e.g. https://github.com/pbrisbin/vim-syntax-shakespeare

plug.vim

@@ -425,8 +425,8 @@ function! s:lod(names, types, ...)
     for dir in a:types
       call s:source(rtp, dir.'/**/*.vim')
     endfor
-    for file in a:000
+    for pat in a:000
-      call s:source(rtp, file)
+      execute 'runtime' pat
     endfor
     if exists('#User#'.name)
       execute 'doautocmd User' name