Make naming of "unnamed" relationships consistent

Previously relationships were named as "   UNNAMED<n>", such that <n>
was:

- For single length relationships with data: the character index
  immediately after the '[';
- For single length relationships without data: the character index
  immediately after the first '-'; or
- For varlength relationships: the character index immediately after the
  end of the preceeding node (either the identifier or the closing
  brace).

This commit makes the <n> consistently refer to the first character in
the relationship declaration, being either '<' or '-'.