sched: Use integer value for select timeout.

sched: Use integer value for select timeout.

This modifies the public struct sched so that users pass in the
default timeout as an integer value in milliseconds rather than
a struct timeval. This simplifies the code a little and eases the
transition from select(2) to poll(2) because poll(2) also takes a
plain integer for the timeout.

Since para_select() of fd.c now calls ms2tv() to convert the timeout
back to a struct timeval, all executables which link with fd.o must
also link with time.o. This was not the case for para_mixer and
para_audioc, so configure.ac needs to be adjusted accordingly.