which makes it possible to add more world language collations
with very complex collation rules (e.g. Myanmar):
- Weight string for a single character in a user defined collation
  was erroneously limited to 7 weights (instead of 8 weights).
  Added an extra element in the user-defined weight arrays,
  to fit 8 non-zero weights.
- Weight string limit for contractions was made two times longer (16 weights),
  which allows longer contractions without affecting the performance
  of filesort.
- A user-defined collation now refuses to initialize and reports an error
  in case if a weight string gets longer than 8 weights for a single character,
  or longer than 16 weights for a contraction. Previously weight strings
  for such characters (and contractions) were cut, so a collation
  could silently start with wrong rules.
- Fixed a bug in handling rules like "&a << b" in combination with
  shift-after-method="expand". The primary weight for "b" was not
  correctly calculated, which erroneously made "b" primary greater than "a"
  instead of primary equal to "a".