* Fix register read bug
If we store a BitVec, we do NOT want to return bool() of it, which
returns True, which is totally incorrect. We do however, want to return
a symbolic Bool of it, if it is a 1 bit register (flag).
* Improve
* Raise error
* Fix register tests
Changed the interfaces:
- removed nbits param (never used)
- no longer raise AssertionError when overflowing a flag reg, just
truncate
- rename test funcs to be more descriptive
* rm unused import
* Add symbolic tests
* Rm no longer applicable test
d0f2c0116e