sasl test: define sasl_callback_ft if not already done so
sasl test: define sasl_callback_ft if not already done so

We could have upped the dependency on libsasl2 but given this is just
a test I thought it wasn't worth the bother of having to make sure
everyone had the newer library version and blah blah blah, so I just
did this.

Signed-off-by: Jonny Lamb <3d1fb3642aaab2ff70e3392a5ab916bf99eed6a3@collabora.co.uk>

noonien-d/wocky,freedesktop-unofficial-mirror/wocky,noonien-d/wocky,freedesktop-unofficial-mirror/wocky,freedesktop-unofficial-mirror/wocky,noonien-d/wocky