Genie:  Don't try fsWrPerm; just use fsRdWrPerm

In Carbon, FSpOpenDF() returns permErr given fsWrPerm.  Since fsRdWrPerm
works in all cases, just use that.

(Additionally, in the unlikely event that open() was called with O_NONE,
use fsRdPerm instead of fsCurPerm.)
Genie:  Clean up whitespace
Genie:  Use fsRdWrShPerm instead of fsRdWrPerm

This is required for POSIX semantics, allowing multiple filehandles open
for writing to the same file.