Add documentation for IBM JRE

Add documentation for IBM JRE

http://publib.boulder.ibm.com/infocenter/iseries/v5r3/index.jsp?topic=/rzaha/rzahajgssusejaas20.htm
http://www.ibm.com/developerworks/java/jdk/security/50/secguides/jgssDocs/api/com/ibm/security/auth/module/Krb5LoginModule.html

Example: -

<application-policy name="host-ibm">
<authentication>
<login-module code="com.ibm.security.auth.module.Krb5LoginModule"
flag="required">
<module-option name="useKeytab">file:///home/darranl/src/negotiation-as/jboss-5.1.0.GA-vm137/bin/service.keytab</module-option>
<module-option name="principal">host/testserver@VM137DOMAIN.GSSLAB</module-option>
<module-option name="credsType">both</module-option>

<module-option name="debug">false</module-option>
</login-module>
</authentication>
</application-policy>

Also see JBAS-4969 the property jboss.security.disable.secdomain.option=true needs to be set.