Bug 691169 - Gimp fails to open files with UTF8 characters as filenames...

...when started via Windows Explorer (e.g. the file context menu)

When built against GLib >= 2.39.90, use g_win32_get_command_line()
and g_option_context_parse_strv() which handle all sorts of windows
filename encodings properly.

(cherry picked from commit 774e064fbf4bc81add8d00182ee677175aa23c55)