New option to get times in agenda zero padded instead of blank padded

New option to get times in agenda zero padded instead of blank padded

Patch by Stephen Eglen, who writes:

> Just a small suggestion here.  In the agenda, an entry like:
> * <2010-01-20 Wed 09:00-09:30> test
>
> gets formatted as follows:
>
> Wednesday  20 January 2010
>               8:00...... ----------------
>  test:        9:00- 9:30 test
>              10:00...... ----------------
>
> the leading whitespace before '9:00' and '9:30' is needed to align the
> times, but having the space after the dash looks odd (at least to my
> latex-trained eyes).  Would it be possible to patch org-agenda to put a
> leading zero rather than leading whitespace.  With this patch, I see:
>
> Wednesday  20 January 2010
>              08:00...... ----------------
>  test:       09:00-09:30 test
>              10:00...... ----------------

This patch introduces a new user option to select this behavior.