get daylight savings time from date('I')

Currently if a user enables "daylight saving time is in effect" in his profile, then an hour is always added to his displayed time. That means it has the same effect as simply choosing a "higher" timezone (e.g. +2 instead of +1) - so twice a year ALL users still have to update their profile and switch the dst flag, which is completely stupid.

Instead, the profile flag should be named "I am affected by dst" and only if the profile flag and date('I') is true, then one hour should be added to the displayed time. That way users affected by dst only have to configure their timezone settings once and users not affected can still disable it.