src/native/vm/VMVirtualMachine.c (unregisterEvent): print error message

src/native/vm/VMVirtualMachine.c (unregisterEvent): print error message

src/native/jvmti/cacaodbg.c (jvmti_cacao_debug_init): set  variable jvmti

src/native/jvmti/VMjdwp.c: add jmethodID and jclass cache variables. Add new callback functions to jvmti_jdwp_EventCallbacks
	(ThreadStart/ThreadEnd/ClassPrepare/Breakpoint): add ThreadStart/ThreadEnd event callbackes implementation who notify jdwp.
	(Exception/MethodEntry): dummy implementation. There are no jdwp exeception/MethodEntry events in gnu classpath yet.
	(setup_jdwp_thread): use cache variables.
	FINDCLASSWITHEXCEPTION/GETMIDWITHEXCEPTION: helper macros to ease jni findclass and getmethodid.
	(fillidcache): new function that fills valid jmethodIDs and jclasses in the cache variables.
	(VMInit): add call to fillidcache.
	(Agent_OnLoad): do not enable all jvmti callbacks anymore. Only enable needed VMInit callback. The other callbacks will be enable with VMVirtualMachine.registerEvent by need.

src/native/jvmti.c (dofireEvent): check if a valid event callback is available before executing it.
	(SetEventNotificationMode): ThreadStart/End event are no more implemented as breakpoints but have direct function calls to dofireEvent.
	(SuspendThread/ResumeThread/getcacaostacktrace): sketch for further implementation of this function. Final threads_suspend* functions are not yet available.
	(GetArgumentsSize):  new implementation using parsed descriptors.
	(GetMethodLocation): add checks for JVMTI_ERROR_NATIVE_METHOD (Samuel Vinson). And return -1 as return values for this dummy implementation.
	(GetJLocationFormat): JLocationFormat probably will be JVMTI_JLOCATION_OTHER

src/native/jvmti/VMjdwp.h: add jdwpthread which stores the thread object for the jdwp listening thread.

src/threads/native/threads.h: remove jvmti_get_threads_breakpoints beacause ThreadStart/End events are implemented as direct function calls by now.

src/threads/native/threads.c (threads_startup_thread): replace ThreadStart/End event implementation.
	(jvmti_get_threads_breakpoints): removed.

src/cacaoh/headers.c (jvmti_fireEvent): added dummy implementation to enable linking of cacaoh.