We did not allocate enough bits for index->trx_id_offset, causing an
UPDATE or DELETE of a table with a PRIMARY KEY longer than 1024 bytes
to corrupt the PRIMARY KEY.

dict_index_t: Allocate enough bits.

dict_index_build_internal_clust(): Check for overflow of
index->trx_id_offset. Trip a debug assertion when overflow occurs.

rb:1380 approved by Jimmy Yang