Do not pad VARBINARY or BINARY columns. (Bug #14189)

innodb.test, innodb.result: Add test cases for foreign key constraints
between VARBINARY and BINARY columns, and between VARCHAR BINARY and
CHAR BINARY columns.

innobase_init(): Assert that
DATA_MYSQL_BINARY_CHARSET_COLL == my_charset_bin.number.

dtype_get_pad_char(): Do not pad VARBINARY or BINARY columns.

row_ins_cascade_calc_update_vec(): Refuse ON UPDATE CASCADE
when trying to change the length of a VARBINARY column
that refers to or is referenced by a BINARY column.  BINARY
columns are no longer padded on comparison, and thus they
cannot be padded on storage either.