[O] Bug: org-capture-templates with %^t

[Matt Lundin]

After commit 51b431d01365211d4c40b07729d5d11d82b9dfe2,
org-capture-templates containing %^t do not work as expected.

The relevant capture template snippet looks like this:

(setq org-capture-templates
      '(("a" "Appointment" entry (file "~/inbox.org") "* %^{Appt}\n %^t%?\n %U\n
%a\n\n %i")))

With this capture template, I am prompted to enter a time via
org-read-date. The expected behavior is as follows:

 - if I enter a date and time of day, the resulting timestamp should 
   contain the time of day:
     - i.e., entering "Thu 8am" should yield "<2017-10-05 Thu 08:00>"
 - if I enter only a date, the resulting timestamp should contain a date
   with no time of day
 - if I enter nothing at the prompt, the resulting timestamp should
   contain today's date with no time of day

What happens now:

 - when I enter a date with a time of day, the timestamp is truncated
   and contains only a date
     - I.e., entering "Thu 8am" now yields "<2017-10-05 Thu>"

This, I think, is counter to the intent of the difference between %^t
and %^T. The lowercase and uppercase (time of day vs. no time of day)
should apply only to the default entry when nothing is entered. But when
the user enters information at the prompt, the behavior should be the
same as that of org-time-stamp, allowing a flexible decision on the fly
as to whether to enter a time of day.

Best,
Matt