INSERT WITH SAME VALUES

Problem:

When a transaction is in READ COMMITTED isolation level, gap locks are still
taken in the secondary index, when row is inserted.  This happens when the
secondary index is scanned for duplicate.  

The function row_ins_scan_sec_index_for_duplicate() always calls the 
function row_ins_set_shared_rec_lock() with LOCK_ORDINARY irrespective of
the transaction isolation level.

Solution:

The function row_ins_scan_sec_index_for_duplicate() calls the 
function row_ins_set_shared_rec_lock() with LOCK_ORDINARY or 
LOCK_REC_NOT_GAP based on the transaction isolation level.

rb://2035 approved by Krunal and Marko