Improve Birthday checking

Hi

For users like me who sometimes run YAM without a restart
it might be very important to rework the Birthday checking
function in YAM so that YAM check the birthday if a new day
is beginning. It could be done in the follow way.

At startup remember the current (old) day.
Call AB_CheckBirthdates() (like now).
Calculate the time until the next day (maybe add some seconds).
Run a Birthday timer with the calculated time.

If the timer triggers then check if old day <> current day and
only if both are different then Call AB_CheckBirthdates()

remember the current (nowold) day.
Calculate the time until the next day (maybe add some seconds).
run a Birthday timer with the calculated time.

In this way the user should not get a reminder twice also if
he change the time or date while YAM is running.

The only remaining issue is that we get the reminder one hour to
late if the DST is changed forward but it happen only once a year.

BTW: you should change some comments in Timer.c. Search for "idn"
and change it to "ion"...