Corrects behavior with `ANISOU` lines in `pdb_selaltloc`

[joaomcteixeira]

Some time ago, #117 improved pdb_selaltloc considerably. Still some cases referring to the ANISOU lines were not covered by the tests which resulted in some bugs -> #130.

From #130, I noticed pdb_selaltloc was also not working properly with residue VU7.

Done in this PR:

• Solved #130 problem with ANISOU lines
• Solved problem with VU7 (7K2U.pdb) like cases found when exploring #130
• all previous tests pass without modification
• added eight more tests

@JoaoRodrigues to my understanding, ANISOU lines do not have information on the occ. Do they? If yes, where?

Should be merged as PATCH.

[amjjbonvin]

Those lines provide anisotropy information - completely different from the ATOM recoords.

@JoaoRodrigues https://github.com/JoaoRodrigues to my understanding, ANISOU lines do not have information on the occ. Do they? If yes, where?

[joaomcteixeira]

Perfect. As I expected. I will add a couple more of tests still.

[joaomcteixeira]

Done. Additional tests and further improvements.