Clean up exception strings and harmonize exception emission

[radiant64]

Currently exception strings are quite messy both in terms of content and nomenclature. Also exception emission behaviour in builtins is not consistent, with the conditions checked for differing quite a lot.

Generally, an exception should be thrown if

• Too few arguments were provided to a function or syntax form.
• Arguments have unexpected types.
• Some type of internal error condition occurs (I/O error, resource allocation fails, out-of-bounds).