use a better timeout which works well also when using the KQUEUE-based iomux implementation

in the kqueue implementation if there are new filedescriptors added by a different thread
while the iomux_run is being run, those are postponed until the iomux_run cycle finished ...
this adds delay if it's running with a big timeout and nothing happens in the meanwhile
to interrupt the kqueue() call

perhaps it's worth allowing to provide the timeout to use at build time so that
the difference between kqueue and epoll can be taken into account (anyway this timeout
value seems a good compromise to not waste too much cpu and let the kqueue-based implementation
be responsive on new connections added to the async mux)
updated libiomux
fixed a test

it wasn't initializing the values to set