should Il g_free string returned by g_filename_to_uft8 andg_filename_from_utf8?

[=?UTF-8?Q?=E8=B5=B5?= =?UTF-8?Q?=E6=89=AC?= <homebody mail1 math pku edu cn>]

as title. the current glib doc (2.2.0) does not mention this. 

Please CC me since I didn't subscribe this list, thanks.
-- 
Zhao Yang <homebody@mail1.math.pku.edu.cn>