atksocket: Fix typo - parameter is _obj not obj. Set freed to NULL.

https://bugzilla.gnome.org/show_bug.cgi?id=699368
Fix an off-by-one in role names

This was causing atk_role_for_name to return ATK_ROLE_LEVEL_BAR
when giving it an empty string, which strangely enough is something
that the lsb testsuite checks...

https://bugzilla.gnome.org/show_bug.cgi?id=704092