Fix for #638 incorrect number of total edges in the status message

My previous pull request #633 (ref #424) had a bug in it which caused incorrect total edge counts whilst building in some restat cases, issue #638. 
The fix reverts the change to the command_edges_ behaviour, and amends the more_to_do function to solving both #633 / #424 and #638.

The variable command_edges_ is the total number of non-phony (command) edges, not the total number of remaining command edges as I had implied from reading the code.