bugfix: unixtimestamp was incorrectly computed

The problem happened in leap year from March til then end
of year and healed itself at the begining of the next year.
During the problem period, the timestamp was 24 hours too
low.

This is primarily a simple fix that can also be applied to
older rsyslog versions. However, we will see if we can
refactor the code to make use of mktime(). Originally, that
was not done for some issues seen, which may no longer
apply.

fixes rsyslog#830

runtime/datetime.c

@@ -1054,6 +1054,11 @@ time_t syslogTime2time_t(struct syslogTime *ts)
 			MonthInDays = 0;	/* any value fits ;) */
 			break;
 	}	
+	/* adjust for leap years */
+	if((ts->year % 100 != 0 && ts->year % 4 == 0) || (ts->year == 2000)) {
+		if(ts->month > 2)
+			MonthInDays++;
+	}
 
 
 	/*	1) Counting how many Years have passed since 1970
@@ -1064,7 +1069,7 @@ time_t syslogTime2time_t(struct syslogTime *ts)
 
 	NumberOfYears = ts->year - yearInSec_startYear - 1;
 	NumberOfDays = MonthInDays + ts->day - 1;
-	TimeInUnixFormat = yearInSecs[NumberOfYears] + NumberOfDays * 86400;
+	TimeInUnixFormat = (yearInSecs[NumberOfYears] + 1) + NumberOfDays * 86400;
 
 	/*Add Hours, minutes and seconds */
 	TimeInUnixFormat += ts->hour*60*60;