Log Message:
libunistring: update to 0.9.10.

New in 0.9.10:
* The functions
    u8_casing_prefix_context, u8_casing_prefixes_context,
    u8_casing_suffix_context, u8_casing_suffixes_context,
    u16_casing_prefix_context, u16_casing_prefixes_context,
    u16_casing_suffix_context, u16_casing_suffixes_context,
    u32_casing_prefix_context, u32_casing_prefixes_context,
    u32_casing_suffix_context, u32_casing_suffixes_context,
  that are documented since version 0.9.1, are now actually implemented.