Add flag to fsargs_Flush to indicate OS_Args flush or close.
On entry to fsargs_Flush r2 will be 1 in a flush, and 0 in a close.
This permits a filing system to correctly implement flushing using OS_Args, but not write back data synchronously on close, which is common behaviour on modern operating systems.
I suggest documenting the remaining bits of r2 as reserved. Would checking FileSwitch version number be sufficient, or do I need to add a OS_FSControl reason code the read FileSwitch features?
Currently RISC OS filing systems are inconsistent as to whether fsargs_Flush is implemented. Further discussion on the forum.