Tests fail on MacOSX (and probably MS Windows)

[rocky]

OS/X doesn't have /dev/full so some of the I/O tests fail.

4405 (83): TEST strm = OpenWrite["/dev/full", BinaryFormat -> True]
----------------------------------------------------------------------
Test failed: BinaryWrite in Reference of Built-in Symbols / File Operations
strm = OpenWrite["/dev/full", BinaryFormat -> True]
Result: OpenWrite[/dev/full, BinaryFormat -> True]
Wanted: OutputStream[...]
Additional output:
General::noopen: Cannot open /dev/full.

4406 (84): TEST BinaryWrite[strm, {39, 4, 122}]
----------------------------------------------------------------------
Test failed: BinaryWrite in Reference of Built-in Symbols / File Operations
BinaryWrite[strm, {39, 4, 122}]
Result: BinaryWrite[OpenWrite[/dev/full, BinaryFormat -> True], {39, 4, 122}]
Wanted: OutputStream[...]

4407 (85): TEST Close[strm]
----------------------------------------------------------------------
Test failed: BinaryWrite in Reference of Built-in Symbols / File Operations
Close[strm]
Output:
General::openx: OpenWrite[/dev/full, BinaryFormat -> True] is not open.
Wanted:
::: No space left on device.

Although I haven't checked, the same is probably true for MS Windows.

We could/should also set up CI testing on MacOSX.

[rocky]

Probably the simplest thing to do is mark OS-specific tests as "sandboxed".