Ensure a consistent netty version

Currently there are clashes between io.netty:netty-common:4.1.0.Beta7 and
io.netty:netty-all:4.1.0.CR3 which can cause errors in the build related
to "VerifyError: Bad type on operand stack".

One solution would be to exclude the jars that duplicate the classes.
However, this can be fragile since additional dependencies may be added
that bring in the dependency transitively.

This commit locks the version for any artifiact with the group "io.nettty"
to ensure the correct version of netty is used.

spring-web-reactive/build.gradle

@@ -26,17 +26,13 @@ repositories {
   maven { url 'http://repo.spring.io/snapshot' }  // Reactor snapshot
 }
 
-configurations.all {
-	// check for updates every build
-	resolutionStrategy.cacheChangingModulesFor 0, 'seconds'
-}
-
 ext {
 	springVersion = '4.2.3.RELEASE'
 	reactorVersion = '2.5.0.M2'
 	reactorNettyVersion = '2.5.0.BUILD-SNAPSHOT'
 	tomcatVersion = '8.0.28'
 	jettyVersion = '9.3.5.v20151012'
+	nettyVersion = '4.1.0.CR3'
 
 	javadocLinks = [
 		"http://docs.oracle.com/javase/8/docs/api/",
@@ -46,6 +42,18 @@ ext {
 	] as String[]
 }
 
+configurations.all {
+	// check for updates every build
+	resolutionStrategy.cacheChangingModulesFor 0, 'seconds'
+	resolutionStrategy.eachDependency { DependencyResolveDetails details ->
+		// consistent netty version to avoid issues with clashes in netty-all vs
+		// netty-common for example
+		if (details.requested.group == 'io.netty') {
+			details.useVersion nettyVersion
+		}
+	}
+}
+
 uploadArchives {
 	repositories {
 		mavenDeployer {