find data (date) gaps in time series

Dear R users,

I have a time series of precipitation data. The time series comprises  
~ 20 years and it is supposed to be constant (one value per day), but  
due to some failure of the measuring device some days or periods are  
missing. I would like to find these missing days or periods just to  
get a first idea about the reliability of the measurements. The only  
function I could find was is.constant(), but of course I only get a  
true or false statement instead of the dates missing.
Google searches and a look at the R help mailing did not reveal an  
answer.

Please find attached a few dates of the time series with missing  
values from February to April. I would like R to detect those missing  
dates.

Any hints or solutions are highly appreciated.

Regards,
Stefan Strohmeier

2916 2002-02-17  0.0
2917 2002-02-18  0.3
2918 2002-02-19  3.8
2919 2002-02-20 43.6
2920 2002-02-21  1.0
2921 2002-02-22  5.6
2922 2002-02-23 10.6
2923 2002-02-24  2.8
2924 2002-02-25 19.1
2925 2002-02-26 20.5
2926 2002-03-06  0.0
2927 2002-05-06  0.0
2928 2002-05-07  0.0
2929 2002-05-08  0.0
2930 2002-05-09  0.0