Exception handler. This function is called by the dispatcher if
a task exception has occured. It is called in the Disable()'d
state so that all signals are still unchanged.
TF_EXCEPT is still set and must be reset by this route.
The exception code is called with the following parameters:
A1 - Task->tc_ExceptData
D0 - Mask of Flags which caused this exception.
A6 - SysBase