docs: Clarify handling of 64-bit integer literals with g_object_new()

As with g_variant_new() (or any varargs function which takes integer literals of differing widths), callers need to be careful to ensure their integer literals have the right width.

Tweak the documentation for g_object_new(), g_object_set() and g_object_get() to clarify this. The documentation for g_object_get() shows that it is not subject to the same caveats, since it operates on pointers.

Signed-off-by: Philip Withnall withnall@endlessm.com

Closes: #833 (closed)