Outputing period (duration) from a template seems to be rather complex.
Also, 'pretty' format with words 'ago', 'in' may be a problem for
outputing duration only .

I create some functions for simplifying this task:
HTMLDate
def periodof(self, pretty=1, othdate='.'):
    """ Render the duration between this date and other date (default is
now). If the "pretty" flag is true, then make the display human readable."""

Interval
def period()
# return interval in human readable format such as "1 month", "2 week" etc.

Use it in templates as:
issue.closedate.periodof(othdate = issue.creation)

Looks like some doc updates to customising.txt are needed
to document the new methods (I searched for reldate to find the
correct location).

Is there anyplace else we need docs?

(I don't think ./doc/html_extra/spec.html needs update, again a historic
document)

Also the templating tests probably need stub definitions
for each of the classes.

Does anybody see aybode se other issues for this patch?

Hi Anthony:

Your patch causes test_dates.py to fail. It returns "in tomorrow" rather
than just "tomorrow" for the interval 1d.

Also intervals "-1d" produces "yesterday ago" but should
return "yesterday".
Also the following intervals fail

        ae('00:00:30', 'in a moment')
        ae('-00:00:30', 'just now')

with "in in a moment" and "just now ago".

They really aren't periods, more a description of the interval
with respect to now.

Ideas on how to fix this?

Tested using: python run_tests.py test/test_dates.py