The ha_innobase table handler contained two search key buffers
(srch_key_val1, srch_key_val2) of fixed size used to store the search
key.  The size of these buffers where fixed at
REC_VERSION_56_MAX_INDEX_COL_LEN + 2.  But this size is not sufficient
to hold the search key.  Hence the following assert in
row_sel_convert_mysql_key_to_innobase() failed.

2438                 /* Storing may use at most data_len bytes of buf */
2439 
2440                 if (UNIV_LIKELY(!is_null)) {
2441                         ut_a(buf + data_len <= original_buf + buf_len);
2442                         row_mysql_store_col_in_innobase_format(
2443                                 dfield, buf,
2444                                 FALSE, /* MySQL key value format col */
2445                                 key_ptr + data_offset, data_len,
2446                                 dict_table_is_comp(index->table));
2447                         buf += data_len;
2448                 }

The buffer size is now calculated with the formula
MAX_KEY_LENGTH + MAX_REF_PARTS*2.  This properly takes into account
the extra bytes needed to store the length for each column.  An index
can contain a maximum of MAX_REF_PARTS columns in it, and for each
column 2 bytes are needed to store length.  

rb://1238 approved by Marko and Vasil Dimov.