Stockflow Improvements

Two jobs were removed from the hard-coded list for DF 0.40, into the custom reactions list.  Instead of deleting those lines, this patch checks the DF version string, allowing this code to work with DF 0.34 if necessary.

Extra error checking has also been added to ensure that stockpiles don't generate an incorrect job if the list gets changed for some reason, and a new flag has been added to make stockflow less reliant on the bookkeeper's speed.