GVariant: add new g_variant_new_take_string() API
Lots of people have variously asked for APIs like
g_variant_new_string_printf() in order to avoid having to use
g_strdup_printf(), create a GVariant using g_variant_new_string(), then
free the temporary string.
Instead of supporting that, plus a million other potential cases,
introduce g_variant_new_take_string() as a compromise.
It's not possible to write:
v = g_variant_new_take_string (g_strdup_printf (....));
to get the desired result and avoid the extra copies. In addition, it
works with many other functions.
https://bugzilla.gnome.org/show_bug.cgi?id=698455