vfs:  Move fixed_dir_extra into header
vfs:  Allow larger 'extra' data in fixed_dir()
Genie:  Allow larger extra data for view delegates
Merge branch 'view-data'
Genie:  Store progress value in delegate's extra
mac -> macos:  Rename for clarity

The new name is more precise, considering that macos implements OS-level
functions.
macos:  Initialize ScrnBase

Other low memory globals will follow.
xv68k:  Axe ScrnBase initialization

Let macos do it.