Foreign key constraint added to acc_trans

["Chris Travers" <..hidden..>]

Hi all;

I have committed changes to the 1.1 codebase that will enforce a
foreign key contraint in acc_trans.chart_id.  I know there are often
concerns about the performance implications of foreign key
constraints, so I want to give people a heads up.

Unlike the post-1.1 changes, I don't expect this to have a real impact
except for better data integrity.  The chart table tends to be small
anyway so the added cost of such a constraint is minimal.

After 1.1 I want to add a foreign key constraint to acc_trans.trans_id
too but this is more likely to run into performance issues down the
road.  Of course this doesn't stop people from dropping the constraint
if necessary, and it is only deferred to after 1.1 in order to ensure
that the existing transaction integrity fixes work properly.

Best Wishes,
Chris Travers