Fix multiple debugger issues. (#1640)

- Wait for free byte code pointers during garbage collection.
- Detect incorrect free requests in the debugger server.
- Ignore byte code blocks loaded from snapshot.
- Use memmove instead of memcpy to avoid receive buffer corruption.

JerryScript-DCO-1.0-Signed-off-by: Zoltan Herczeg zherczeg.u-szeged@partner.samsung.com

jerry-core/jcontext/jcontext.h

@@ -88,6 +88,7 @@ typedef struct
   uint8_t debugger_send_buffer[JERRY_DEBUGGER_MAX_BUFFER_SIZE]; /**< buffer for sending messages */
   uint8_t debugger_receive_buffer[JERRY_DEBUGGER_MAX_BUFFER_SIZE]; /**< buffer for receiving messages */
   jmem_cpointer_t debugger_byte_code_free_head; /**< head of byte code free linked list */
+  jmem_cpointer_t debugger_byte_code_free_tail; /**< tail of byte code free linked list */
   int debugger_connection; /**< hold the file descriptor for socket communication */
   uint8_t debugger_flags; /**< debugger flags */
   vm_frame_ctx_t *debugger_stop_context; /**< stop only if the current context is equal to this context */