weather-yahoo plugin crashes in some locales

[Nuno Araujo]

According to the locale configuration of the computer, the weather-yahoo plugin crashes.

This happens when parsing the sunrise and sunset times.
According to the python documentation, the strptime method takes the current application locale into account when doing it's parsing. This method fails as below if e.g the LC_TIME env var is set to fr_CH.utf8

Traceback (most recent call last):
  File "/usr/share/gnome15/plugins/weather/weather.py", line 240, in refresh
    self._weather = backend.get_weather_data()
  File "/usr/share/gnome15/plugins/weather-yahoo/weather-yahoo.py", line 156, in get_weather_data
    return self._do_get_weather_data_xml()
  File "/usr/share/gnome15/plugins/weather-yahoo/weather-yahoo.py", line 228, in _do_get_weather_data_xml
    sunset = time.strptime(astronomy["sunset"], "%I:%M %p")
  File "/usr/lib/python2.7/_strptime.py", line 454, in _strptime_time
    return _strptime(data_string, format)[0]
  File "/usr/lib/python2.7/_strptime.py", line 328, in _strptime
    data_string[found.end():])
ValueError: unconverted data remains: pm