Exceptions (DAB/PAB/UND) are not handled correctly if user handlers are registered

All Exceptionhandlers choose the wrong handler (HalExpt_MainSwitchCode). USR Handler is called in Systemmode, while SYS handler is called for all other modes. Currently I don't see any reason why to seperate USR/SYS handler this way.

Prefetch Abort does not work at all due to this error, as the undefined _USR handler is called, when the exception is thrown in System Mode (which is default for rcX V2 tasks).

When Exception is thrown in user mode, it results in an undefined instruction, as the handler switches back to user mode (unpriviledged) and tries to read cp15 registers which is forbidden in this mode.