#398 Fix double DST occurrences #404
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Simplify the method we use for calculating time changes across DST boundaries by performing arithmetic under UTC to get "absolute" values. This is a revert of the "unrolling in pairs" method introduced in c93fa7e for fixing ice-cube-ruby#189. The method of converting to UTC and back for doing time arithmetic only applies when DST needs to be taken into consideration. For rules with less than daily intervals, both hours still need to occur. This distinction was added in the original fix. However, the method was not correctly tested for non-ActiveSupport times (local system TZ) and the advancing of time to the next occurrence was validating both the last DT hour (before fall back) and first ST hour (after fall back) causing double occurrences for the "same" hour on the clock face. Fixes ice-cube-ruby#398
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Simplify the method we use for calculating time changes across DST boundaries by
performing arithmetic under UTC to get "absolute" values. This is a revert of
the "unrolling in pairs" method introduced in c93fa7e for fixing #189.
The method of converting to UTC and back for doing time arithmetic only applies
when DST needs to be taken into consideration. For rules with less than daily
intervals, both hours still need to occur. This distinction was added in the
original fix.
However, the method was not correctly tested for non-ActiveSupport times (local
system TZ) and the advancing of time to the next occurrence was validating both
the last DT hour (before fall back) and first ST hour (after fall back) causing
double occurrences for the "same" hour on the clock face.