More bugfixes throughout project

- I had forgotten to give semi-infinite type C words the 'type_b_data'
- I had mistakenly decided share_orbit(u, u) should return \Z
- Fencepost error in the periodic version of share_orbit
- sign error in _check_for_ponds()
- widened the try block in _potential_conjugators(). Errors (e.g. gen
sets that aren't bases) can be raised before ceating the Automorphism
instance