add a neocomplcache configuration for using it with tpope/vim-rails

avoid the following error;
  ^@  completefunc=syntaxcomplete#Complete^@^ILast set from ~/.vim/bundle/neocomplcache/autoload/neocomplcache/init.vim
  Another plugin set completefunc! Disabled neocomplcache.

ref. http://d.hatena.ne.jp/senggonghaza/?via=201007