Returned values in A after various OSARGS calls
              -----------------------------------------------

Documentation says that OSARGS should return A preserved if the call is
unsupported, and should return zero or a return value if the call is
supported. Also, the Advanced Econet User Guide states that PTR= (and, by
implication EXT=) should return zero only if the file has been extended.
This lists actual return values.

              OSARGS Y=0                                OSARGS Y<>0
              A ON EXIT                                  A ON EXIT
        A  DFS NFS33 NFS36 ANFS ADFS HADFS         A  DFS NFS ANFS ADFS HADFS
FC                     FC            FC                    FC           FC
FD     FD:  FD   FD    FD   FD   00  3C    FD     FD:  FD  FD  FD   00  00
DRIVE  FE:  FE   FE    FE   FE   00  04    INFO   FE:  FE  FE  FE   00  00
ENSURE FF:  00   FF    FF   FF   00  00    ENSURE FF:  00  FF  FF   00  00
FSNUM  00:  04   05    05   05   08  10    =PTR   00:  00  00  00   00  00
CLINE  01:       00    00            00    PTR=   01:  00  00  00   00  00/FF
VERS   02:       02    01            00    =EXT   02:  00  00  00   00  00
LIBFS  03:       03    03            10    EXT=   03:  00  03  00   00  00/FF
USED   04:  04   04    04   00   00  00    =ALLOC 04:  04  04  00   00  00
FREE   05:  05   05    05   05   00  00    =EOF   05:  05  05  05   00  00
06     06:  06   06    06   06   00  06    ALLOC= 06:  06  06  06   00  00
07                     07            07                    07           07
80     80:  80   80    80  error 00  80    HANDLE 80:  80  80  00   00  80

On the Master, OSARGS 0-3,0 are implemented by FileSwitch, and so always
return the following, regardless of what the filing system itself returns:
    0 FSNUM   returns A=FSNUM      2 VERS  returns A=&01
    1 CMDLINE returns A=&DC        3 LIBFS returns A=LIBFS or &FF

This shows various things:

* NFS and ANFS return A=&FF on ENSURE, implying the call is not implemented.
This is effectively correct on NFS as channels are not buffered locally, but
ANFS does buffer files, so should return A=&00.

* ANFS claims it supports USED, but the value returned at !X is unchanged.

* NFS and ANFS ignore the documentation and return A=&00 on PTR= and EXT=,
implying file extended past its previous length.

* It clearly shows that NFS does not support EXT= and ANFS does.

* It also shows that ANFS supports =ALLOC, which I have only ever seen
documented in the SJ MDFS manual.

* Documentation claims that ANFS 4 returns A=0 for VERS. ANFS 2.x returns
A=&01, but on the Master the call is handled by FileSwitch which also
returns A=&01. ANFS 4.0x on the BBC returns A=&01 as with NFS 3.6x.

* ANFS doesn't check for the handle<>0 on HANDLE as it generates the error:
"Net channel on 0"

* ADFS claims that is supports everything by erroneously returning &00 for
absolutely everything! The only reason the Y=0 calls do not return A=&00 is
because FileSwitch on the Master deals with these calls itself.

* HADFS is the only system that complies with the documentation stating that
A<>&00 if the file has not been extended after PTR= or EXT=.