* Fix #8569: XBT/synchro.h has redundant declarations
* Fix #8563: MSG return values and exceptions
Introduce a MSG_TIMEOUT_FAILURE return code and use it consistently.
* Fix #8569: XBT/synchro.h has redundant declarations
* Fix #8563: MSG return values and exceptions
Introduce a MSG_TIMEOUT_FAILURE return code and use it consistently.