Limited ThreadLocal value support

By default, every Java call made using the mosjvm module occurs in a separate Java thread that is terminated after the Java method completes. This means that you cannot use ThreadLocal objects to share values between multiple jvmcall<type> invocations from the same model. However, if you force Java calls from Mosel to fire on the same Java thread by using the jvmattachthread procedure, then ThreadLocal values can be used.