Change hash_sort to take in and return uint64 instead of ulong, as ulong is
32-bit on Windows, which gives us different hash values on different platforms.
(MySQL Cluster also wants 64-bit hash values, regardless of platforms.) For
code that needs stability on disk, so that hash values cannot change, we
truncate to ulong on input and output. (This is safe; see the next paragraph.)

Stability with previous versions have been verified by running the unit test
against the current mysql-trunk, casting the expected result to ulong, both on
Windows and on Linux. In addition, each hash function has been manually
inspected to check that it either works in uint64 internally (the Unicode 9.0
collations) or only propagates bits upwards (all other collations), which means
that it doesn't matter whether we truncate during the computations or once at
the end.

Change-Id: I2ab1ca7554efb0c00eca73da0cb22fcf10f1e761
(cherry picked from commit b03661eaae37429ef91a71906a0b5f52191b7dfd)