Blender Git Loki

Remove G.save_over

The difference between G.save_over and G.relbase_valid was minor.

There is one change in functionality. When saving the default-startup
file from an already loaded blend file - future save actions will
continue to write to the originally loaded file instead of prompting
the user to select a location to save the file.

This change makes saving the startup file behave the same way
"Save a Copy" does.

Reviewed By: brecht

Ref D13556