proxy: case insensitive compare of Expect: 100-continue header (#1922)

From the RFC:  "Comparison of expectation values is case-insensitive for unquoted tokens (including the 100-continue token), and is case-sensitive for quoted-string expectation-extensions. "

Signed-off-by: Steven Schlansker <stevenschlansker@gmail.com>

jetty-proxy/src/main/java/org/eclipse/jetty/proxy/AbstractProxyServlet.java

@@ -433,7 +433,7 @@ protected boolean hasContent(HttpServletRequest clientRequest)
 
     protected boolean expects100Continue(HttpServletRequest request)
     {
-        return HttpHeaderValue.CONTINUE.asString().equals(request.getHeader(HttpHeader.EXPECT.asString()));
+        return HttpHeaderValue.CONTINUE.is(request.getHeader(HttpHeader.EXPECT.asString()));
     }
 
     protected void copyRequestHeaders(HttpServletRequest clientRequest, Request proxyRequest)