Support current version of dcd, and a little bug fix

* Update to follow current DCD.  
`ac-dcd-adjust-cursor-on-completion` is called on completion if the dcd is newer than 4.0. It will make the completion work on this version.

* Bug fix: multiple ac-dcd-flags was not accepted. 
If more than one ac-dcd-flags were set, they were unescaped and regarded as one flag. Now it's fixed.
Any particular reason to prefer `string-match` over `equal`?