Monitor exceptions, re-decoding the instruction in this case

Monitor exceptions, re-decoding the instruction in this case

The misaligned load test-case now passes.

Whenever an exception is reported during Execution, it is forwarded to
PowerDecode2. After Execution finishes, Issue notices this, and returns
directly to Decode, without updating PC, SVSTATE, etc. The exception
condition is always cleared after a Decode, to prepare the stage for
a new Execution.