Improve changes() and total_changes() functions and add tests

[ben594]

#144

• The previous changes() function returns 1 no matter what
• Modified changes() and total_changes() to be closer to the sqlite implementation
  • Store local n_change counter in the Program struct
  • Update last_change and total_changes values in Connection struct on halt
  • Add change_cnt_on flag to Program struct that is true for insert and delete (also need later on for update)
• Added TCL tests