Limiting versions that trigger !STABLE warning

+ Only RC# and M# trigger warning now.
+ Warning includes URL for where to download stable version.

jetty-server/src/main/java/org/eclipse/jetty/server/Server.java

@@ -344,7 +344,10 @@ public class Server extends HandlerWrapper implements Attributes
 
         LOG.info("jetty-" + getVersion());
         if (!Jetty.STABLE)
+        {
             LOG.warn("THIS IS NOT A STABLE RELEASE! DO NOT USE IN PRODUCTION!");
+            LOG.warn("Download a stable release from http://download.eclipse.org/jetty/");
+        }
         
         HttpGenerator.setJettyVersion(HttpConfiguration.SERVER_VERSION);
         MultiException mex=new MultiException();

jetty-util/src/main/java/org/eclipse/jetty/util/Jetty.java

@@ -33,16 +33,11 @@ public class Jetty
             VERSION = pkg.getImplementationVersion();
         else
             VERSION = System.getProperty("jetty.version", "9.3.z-SNAPSHOT");
-        
+
         POWERED_BY="<a href=\"http://eclipse.org/jetty\">Powered by Jetty:// "+VERSION+"</a>";
-        
-        boolean stable=true;
-        for (char c: VERSION.toCharArray())
-        {
-            if (c!='.' && !Character.isDigit(c))
-                stable=false;
-        }
-        STABLE=stable;
+
+        // Show warning when RC# or M# is in version string
+        STABLE = !VERSION.matches("^.*\\.(RC|M)[0-9]+$");
     }
 
     private Jetty()