[Shotwell] Pretty-printed date ranges not so pretty as previously thought...let's fix it!

[Clinton Rogers]

Good afternoon, one and all,

Apologies for bothering the list, but we recently encountered an issue
where events spanning exactly two days would display their date range
incorrectly for certain languages and locales, leading to, say, the
fourteenth and fifteenth of February in 1999 displaying nicely when
run under en_US, but occasionally producing something like:
-    Wednesday, 14 Feb-15, 1999 (en_GB)
    -or-
-    2月14日月1999年 (ja_JP)
...or something equally nonsensical when running under other LANG
settings.  Although we think we've remedied the problem now, it would
be beneficial to have other pairs of eyes looking at this, and so, we
turn to you.

How to reproduce the problem:
1) Place any two images in an event together.
2) Set one of the image's timestamp to a given date and time, say 4 March 2003.
3) Set the other image's date to 5 March 2003.
4) Next, have a look at the event in the sidebar.

If you see something like (depending on your locale) Monday 4-5 Mar,
2003, then the application is functioning as intended, and no change
is needed, but if you see anything weird here at all, please let us
know.  Part of our goal for Shotwell is to have the nicest user
experience possible, and that includes not displaying gibberish for
dates and times.

Cheers,
-c