DESCRIPTION:
------------

 1) When attempting to create a table partitioned by key,
    using only prefixed columns used as part of the
    primary/unique key, the user gets a confusing error
    message.

    eg: mysql> CREATE TABLE `t1` (
        ->         `a` VARCHAR(100),
        ->         `b` VARCHAR(25),
        ->         PRIMARY KEY (a(10), b(2))
        ->     ) PARTITION BY KEY() PARTITIONS 2;
    ERROR 1503 (HY000): A PRIMARY KEY must include all
    columns in the table's partitioning function

 2) The partitioning function has always ignored prefixed
    columns in the PRIMARY/UNIQUE KEY, for its partition
    calculations. The warning message added for the
    deprecation of this syntax in WL#13588 could be improved
    to make this clear.

    eg: mysql> CREATE TABLE `t2` (
        ->         `a` VARCHAR(100),
        ->         `b` VARCHAR(25),
        ->         PRIMARY KEY (a(10), b)
        ->     ) PARTITION BY KEY() PARTITIONS 2;
    Warning 1681: Usage of column 'test.t2.a' having prefix
    key part 'a(10)' in the PARTITION BY KEY() clause is
    deprecated and will be removed in a future release.

FIX:
----

 1) The error message ER_UNIQUE_KEY_NEED_ALL_FIELDS_IN_PF is
    changed to be inclusive of this case to avoid confusion.

    eg: ERROR 1503 (HY000): A PRIMARY KEY must include all
    columns in the table's partitioning function (prefixed
    columns are not considered).

 2) The warning message in
    ER_WARN_CLIENT_DEPRECATED_PARTITION_PREFIX_KEY and
    ER_WARN_LOG_DEPRECATED_PARTITION_PREFIX_KEY is improved.

    eg: Warning 1681: Column 'test.t2.a' having prefix key
    part 'a(10)' is ignored by the partitioning function.
    Use of prefixed columns in the PARTITION BY KEY() clause
    is deprecated and will be removed in a future release.

Change-Id: Iedaa4bca503c4f76b65705aa16fd2c9d7ff979c0