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
2a0a6a0541