The previous way of splitting strings would break if the last string in
the line was an empty string, and it would return one fewer fields than
it should have. This was breaking the last line in the
scripts.base.framework.input.ascii.setspecialcases once the bug fixed in
GH #1628 was fixed.
Escaped ,'s in sets and vectors were unescaped before tokenization
Handling of zero-length-strings as last element in a set was broken (sets ending with a ,).
Hashing of lines just containing zero-length-strings was broken (now a \0 is appended to each
string before it is hashed - giving us a hash of something for a line just consisting of \0s.
This also allows to differentiate between vectors with varying numbers of zero-length-strings).
