mysql-55-eb allows invalid per-index KEY_BLOCK_SIZE values

Now that per-table KEY_BLOCK_SIZE has a meaning with HEAP tables, the engine should also handle or reject per-index KEY_BLOCK_SIZE. Right now, the following statement:

 CREATE TABLE t1 (f1 VARCHAR(512), KEY (f1) KEY_BLOCK_SIZE=12) ENGINE=HEAP ROW_FORMAT=DYNAMIC KEY_BLOCK_SIZE=1024;

returns OK and KEY_BLOCK_SIZE=12 is preserved in SHOW CREATE TABLE even though it is too small to accomodate a VARCHAR(512) column.

If the same statement is issued against MyISAM, the value of KEY_BLOCK_SIZE will be automatically updated to a valid one.