Add error message to jconsole.sh if JAVA_HOME not set and terminate the script

jconsole.sh does not work on Mac OSX:

Jim-Tyrrells-MacBook-Pro-2:bin jimtyrrell$ ./jconsole.sh
CLASSPATH /lib/jconsole.jar:/lib/tools.jar:/Users/jimtyrrell/Servers/eap6beta2/jboss-eap-6.0/modules/org/jboss/remoting3/remoting-jmx/main/remoting-jmx-1.0.3.CR1-redhat-0-todo.jar:/Users/jimtyrrell/Servers/eap6beta2/jboss-eap-6.0/modules/org/jboss/remoting3/main/jboss-remoting-3.2.4.GA-redhat-1.jar:/Users/jimtyrrell/Servers/eap6beta2/jboss-eap-6.0/modules/org/jboss/logging/main/jboss-logging-3.1.0.GA-redhat-1.jar:/Users/jimtyrrell/Servers/eap6beta2/jboss-eap-6.0/modules/org/jboss/xnio/main/xnio-api-3.0.3.GA-redhat-1.jar:/Users/jimtyrrell/Servers/eap6beta2/jboss-eap-6.0/modules/org/jboss/xnio/nio/main/xnio-nio-3.0.3.GA-redhat-1.jar:/Users/jimtyrrell/Servers/eap6beta2/jboss-eap-6.0/modules/org/jboss/sasl/main/jboss-sasl-1.0.0.Final-redhat-1.jar:/Users/jimtyrrell/Servers/eap6beta2/jboss-eap-6.0/modules/org/jboss/marshalling/main/jboss-marshalling-1.3.13.GA-redhat-1.jar:/Users/jimtyrrell/Servers/eap6beta2/jboss-eap-6.0/modules/org/jboss/marshalling/river/main/jboss-marshalling-river-1.3.13.GA-redhat-1.jar:/Users/jimtyrrell/Servers/eap6beta2/jboss-eap-6.0/modules/org/jboss/as/cli/main/jboss-as-cli-7.1.1.Final-redhat-1.jar:/Users/jimtyrrell/Servers/eap6beta2/jboss-eap-6.0/modules/org/jboss/staxmapper/main/staxmapper-1.1.0.Final-redhat-1.jar:/Users/jimtyrrell/Servers/eap6beta2/jboss-eap-6.0/modules/org/jboss/as/protocol/main/jboss-as-protocol-7.1.1.Final-redhat-1.jar:/Users/jimtyrrell/Servers/eap6beta2/jboss-eap-6.0/modules/org/jboss/dmr/main/jboss-dmr-1.1.1.Final-redhat-1.jar:/Users/jimtyrrell/Servers/eap6beta2/jboss-eap-6.0/modules/org/jboss/as/controller-client/main/jboss-as-controller-client-7.1.1.Final-redhat-1.jar:/Users/jimtyrrell/Servers/eap6beta2/jboss-eap-6.0/modules/org/jboss/threads/main/jboss-threads-2.0.0.GA-redhat-1.jar:/Users/jimtyrrell/Servers/eap6beta2/jboss-eap-6.0/modules/org/jboss/as/controller/main/jboss-as-controller-7.1.1.Final-redhat-1.jar
Exception in thread "main" java.lang.NoClassDefFoundError: sun/tools/jconsole/JConsole
Caused by: java.lang.ClassNotFoundException: sun.tools.jconsole.JConsole
at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
at java.lang.ClassLoader.loadClass(ClassLoader.java:247)