Fix : Can't handle CJK multibyte request in AJP parameter value

### Problem :

In HTTP protocol hander can handle multibyte character set. My case use EUC-KR character set.  Tested in Wildfly 8.2 GA.
```xml
            <server name="default-server">
                <ajp-listener name="ajp" socket-binding="ajp" url-charset="EUC-KR"/>
                <http-listener name="default" socket-binding="http" url-charset="EUC-KR"/>
```
http://localhost:8080/test/test.jsp?param=한글

But, When I use AJP protocol can't handle EUC-KR character set.
http://localhost/test/test.jsp?param=한글

Query param's value are not '한글', it  prints '??'.
Similar cases are in https://developer.jboss.org/thread/242677?start=0&tstart=0

### Reason :

I found that it cause of handle byte as a char in AbstractAjpParser. 
Multibyte(CJK ; Chinese, Japanese, Korean) character set are use most significant bit. So, when byte are casted to char, multibytes informations are eliminated.

Thanks for your great **'undertow'**.