Detailed revision comments:

r6536 | sunny | 2010-01-30 00:13:42 +0200 (Sat, 30 Jan 2010) | 6 lines
branches/5.1: Check *first_value everytime against the column max
value and  set *first_value to next autoinc if it's > col max value.
ie.  not rely on what is passed in from MySQL.

[49497] Error 1467 (ER_AUTOINC_READ_FAILED) on inserting a negative value
rb://236