tyru 63074a52ad Avoid E403 error on :syn-include ...

Example .vimrc:

        let g:markdown_fenced_languages = ['vim', 'viml=vim']
        syntax on

causes

        "/tmp/test.mkd" 6L, 98C
        Error detected while processing /usr/share/vim/vim74/syntax/vim.vim:
        line  777:
        E403: syntax sync: line continuations pattern specified twice
        E403: syntax sync: line continuations pattern specified twice

Example "test.mkd" file:

        ```vim
        echo 'hi'
        ```

2016-01-23 02:09:00 +09:00

..

markdown.vim

Avoid E403 error on :syn-include

2016-01-23 02:09:00 +09:00