This reverts commit 011257dc88.
This commit was not working properly. Attempts are made to fix it,
but so close to 1.9, it sounds a lot better to revert it from the
1.9 branch, and keep developing it further in 1.10.
Allow multiple AIs to possibly start in the same tick.
start_date = 0 becomes a special case, where random deviation does not occur.
If start_date was not already 0, then a minimum value of 1 must apply.
