message: Fix new functions in agent headers.
diff: @@ -11,7 +11,8 @@ extern indy_error_t indy_prep_msg(indy_handle_t command_handle,
  const indy_u8_t *const msg_data,
  indy_u32_t msg_len,
  - void (cb*)(const indy_u8_t *const encrypted_msg
  + void (cb*)(indy_handle_t command_handle,
  + const indy_u8_t *const encrypted_msg
  indy_u32_t encrypted_len)
  );
  @@ -20,7 +21,8 @@ extern indy_error_t indy_prep_anonymous_msg(indy_handle_t command_handl
  const indy_u8_t *const msg_data,
  indy_u32_t msg_len,
  - void (cb*)(const indy_u8_t *const encrypted_msg
  + void (cb*)(indy_handle_t command_handle,
  + const indy_u8_t *const encrypted_msg
  indy_u32_t encrypted_len)
  );
  @@ -29,7 +31,8 @@ extern indy_error_t indy_parse_msg(indy_handle_t command_handle,
  const indy_u8_t *const encrypted_msg,
  indy_u32_t encrypted_len,
  - void (cb*)(const char *const sender_vk,
  + void (cb*)(indy_handle_t command_handle,
  + const char *const sender_vk,
  const indy_u8_t *const msg_data,
  indy_u32_t msg_len)
  );
  