intervals() calculates negative means on long chronologies

[chguiterman]

Based on how R sorts years when their length changes, composite() places pre-1000 CE dates after post-1000 CE dates. This results in intervals() calculating negative (and totally erroneous besides) intervals. For example,

The second column are years, and note that the year 817 CE comes after 1879 CE. This results in -1062 year interval...

To fix it, I'll sort the years entering intervals()

[brews]

Man, thanks for catching this, @chguiterman 👍