An absolute wake time is now calculated and updated by set_server_bits(),
TimerTimeout() and tclTimerTimeout(). This is then used to calculate the actual
select() timeout, instead of having those functions calculate a relative timeout
value themselves. This significantly simplifies those functions, since the
underlying values tend to be recorded as absolute times.
It also allows us to disentangle tclTimeTimeout from TimerTimeout(), and move the
responsibility for calculating the QUEUE_SENDS wake time from TimerTimeout() to
set_server_bits() where it belongs.
The QUEUE_SENDS and CONNECT_DELAY wake up times will also now be correctly
calculated, based on the last sent time and connect time respectively.
Define USE_NON_CONST so that the newer TCL headers define functions in the
same way as pre-8.4 TCL headers. It will be a good idea to change to
USE_COMPAT_CONST instead at some point.
Also use ckfree() instead of free() to free an allocation returned by TCL.
