mariadb10.0.4: enable MYSQL_TYPE_XXX2 time related types

MariaDB 10.0.4 backports them from MySQL 5.6. But MariaDB 10.0.4
doesn't use these types. It just uses them for reading MySQL 5.6 data.

This change fixes the following warnings:

    ha_mroonga.cpp: In function ‘grn_builtin_type mrn_grn_type_from_field(grn_ctx*, Field*, bool)’:
    ha_mroonga.cpp:950:10: warning: enumeration value ‘MYSQL_TYPE_TIMESTAMP2’ not handled in switch [-Wswitch]
       switch (mysql_field_type) {
              ^
    ha_mroonga.cpp:950:10: warning: enumeration value ‘MYSQL_TYPE_DATETIME2’ not handled in switch [-Wswitch]
    ha_mroonga.cpp:950:10: warning: enumeration value ‘MYSQL_TYPE_TIME2’ not handled in switch [-Wswitch]
    ha_mroonga.cpp: In member function ‘void ha_mroonga::storage_store_field(Field*, const char*, uint)’:
    ha_mroonga.cpp:9724:10: warning: enumeration value ‘MYSQL_TYPE_TIMESTAMP2’ not handled in switch [-Wswitch]
       switch (field->real_type()) {
              ^
    ha_mroonga.cpp:9724:10: warning: enumeration value ‘MYSQL_TYPE_DATETIME2’ not handled in switch [-Wswitch]
    ha_mroonga.cpp:9724:10: warning: enumeration value ‘MYSQL_TYPE_TIME2’ not handled in switch [-Wswitch]
    lib/mrn_multiple_column_key_codec.cpp: In member function ‘void mrn::MultipleColumnKeyCodec::get_key_info(KEY_PART_INFO*, mrn::MultipleColumnKeyCodec::DataType*, uint*)’:
    lib/mrn_multiple_column_key_codec.cpp:294:12: warning: enumeration value ‘MYSQL_TYPE_TIMESTAMP2’ not handled in switch [-Wswitch]
         switch (field->real_type()) {
                ^
    lib/mrn_multiple_column_key_codec.cpp:294:12: warning: enumeration value ‘MYSQL_TYPE_DATETIME2’ not handled in switch [-Wswitch]
    lib/mrn_multiple_column_key_codec.cpp:294:12: warning: enumeration value ‘MYSQL_TYPE_TIME2’ not handled in switch [-Wswitch]