Improve error signalling for seq-subseq.
The existing behaviour for seq-subseq is to error when indexes are too large, but to silently ignore numbers which are too negative for lists. String and vector handling errors in both cases. This has been regularlised. Error signalling behaviour has been explicitly added to the docstring of seq-subseq, and also to cl-subseq which largely defers to seq-subseq (and is therefore also impacted by this change). Tests have been added for these exceptional cases, as well as one non exceptional base case.
Showing with 15 additions and 3 deletions