Scheduled Transactions rewrite

[Andrew Duggan]

Hi,

A bit delayed, but I wanted to say thanks for the the new sx code. Dealing 
with the list is much simpler now with the combination of

     inst_model = gnc_sx_get_current_instances();
     gnc_sx_instance_model_summarize(inst_model, &summary);

My custom feature of a pending sx tool button that displays the number of 
pending sx, was reduced by about 280 lines.

Nicely done.  The new since last run dialog is really nice. Great job.

Andrew