This version of chron has fixed a bug in converting from the internal
julian representation to the abbreviated string output format.

It also provides a mechanism for dealing with 2-digit dates.

The option 'chron.year.abb', 'TRUE' by default, specifies that 2-digit
years are to be interpreted as an abbreviated form.  The option
'chron.year.expand' is a function that takes this numeric representation
and returns full expanded years (or aborts the computations).  We
provide the functions year.strict() and year.expand(), the first one
simply aborts the task, the second one adds either 1900 or 2000 to the
2-digit integer depending on its arguments 'cut.off = 30' and 'century =
c(1900, 2000)'.