Log Message:
Backgrond printing works again:

https://github.com/rdmark/Netatalk/pull/1/commits/1d289cc41e810748237e2
6518d8f9b57954f5875

Allow a session tickleval of 0 instead of -1.  Based on the following commit:
https://github.com/rdmark/Netatalk/commit/0b4e290ac5343df093cbaef9c5ebcbc11ee -
912a2#diff-ac91c62802b4ac4bd19ade9f9b2ed99e07560281f11655038ee85b6f628cb1c1

These patches were supplied by Daniel Markstedt (rdmark) from his fork of
Netatalk22.