dstfail-934098: Allow test inaccuracy of 1 hour for DST changes

Tests that look at yesterday and tomorrow are allowed to have an
additional fuzz of 1 hour to cope with daylight savings time (no
countries currently do more than 1 hour [1]) and we can't code this
module to cope with all possible changes to DST.

[1]: http://en.wikipedia.org/wiki/Daylight_saving_time