open_memstream on non-linux?

[Henrik Brautaset Aronsen]

Miika's commit 42ea5e35 contains

    f = open_memstream(&membuf, &streamsize);

in divelist.c, but open_memstream doesn't seem to be supported on Mac 
(or Windows[1])

Henrik

[1] http://stackoverflow.com/a/10341073/13365