the lag / skipping of the clock was not caused by faulty timer code
on fluxbox's side but by the behavior and inner workings of time().
since this is fixed now (913244789f) we can now rollback ec7fe513c8
and detect strftime-formats which need intervals of seconds or minutes.
minor: the small change to FbTk::Timer::setTimeout() reduces one
start() / stop() cycle for a running timer.
Do not try to be too smart which compilations need config.h, as most of
them will simply because of the config.h has information about system
capabilities.
* Calling Timer::setTimeout() from within Timer::start() might lead to ugly
behavior (as experienced in bugs #3590078, #3600143, etc; see commit
4d307dcd10, fixes the problem partially).
* Stop a timer first, then call the handler (via Timer::fireTimeout()). A
given handler might call Timer::start() again, which (re)adds the Timer
to the control list .. the following Timer::stop() would remove it again.
* Use 'm_start' as indicator if timer is running.
* Move the (now quite short) code of ::addTimer / ::removeTimer
into the Timer::start() and Timer::stop() functions.
gettimeofday() is subject to be changed on daylight-saving or to ntp-related
(think leap-seconds). even worse, it is subject to be changed BACK in time. this
is hard to fix correctly (see commit 45726d3016 and bug #3560509). it is
irrelevant for timers to know the nano-seconds since the epoch anyways.
