If a file's data is already available in Blender, it might be changed.
For example, an internal text datablock or a changed text file. We need
to use those overrides.
Age output files are now handled in all aspects by a singleton manager.
This allows us to track all generated files and external dependency
files and ensure they are correctly copied over to the target game... Or
not, in the case of an age/prp export from the File > Export menu.
Currently only SFX files are handled as an external dependency. TODO are
python and SDL files.
Further, because we have an output file manager, we can bundle all the
files into a zip archive for releasing the age in one step. Wow such
amazing. ^_^