DASH: fix compatibility with com.sun.net.httpserver

modules/stream_filter/dash/http/HTTPConnection.cpp was case-sensitive
when checking Content-Length.  RFC 2616 section 4.2 states "Field names
are case-insensitive"

The http server built in to the JDK 1.6 uses a field name of
"Content-length" which reveals an incompatibility of VLC's DASH module.
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

modules/stream_filter/dash/http/HTTPConnection.cpp

@@ -119,7 +119,7 @@ bool            HTTPConnection::parseHeader     ()
 
     while(line.compare("\r\n"))
     {
-        if(!line.compare(0, 14, "Content-Length"))
+        if(!strncasecmp(line.c_str(), "Content-Length", 14))
             this->contentLength = atoi(line.substr(15,line.size()).c_str());
 
         line = this->readLine();