Stripping the header date from the semicolon-separated extensions before parsing

Having deployed an application to a Wildfly AS (powered by Undertow 1.0.0) I realized that it fails to parse _If-Modified-Since_ header passed by Internet Explorer 9. The header value contains additional "length" parameter after a semicolon, which causes the date parsing routine to fail. 

I propose a fix of removing a trailing semicolon and everything that comes after it before attempting to parse the date in *DateUtils* class. I'm attaching a simple test suite that parses the _If-Modified-Header_ sent by three major browsers.