bind to port 0 in place of a random port

[turbio]

When binding to a variable port the strategy is to choose a random port. This sounds like a real bad idea leading to random errors and other fun.

Should instead bind to port 0 in all cases where we currently listen randomly as this lets the os choose a suitable port.

[boehs]

0 is too special, I propose 15319, the date of the initial commit (2015-3-19)