Fix bug introduced with refactoring of object mirroring API to libgeda.
When reading a complex object from file, the mirror property of the
complex is set to the desired value and later code then mirrors the
prim_objs which make up the complex. o_complex_mirror_world() was used
by mistake, where o_list_mirror_world() should have been used.
This could be refactored so that complex creation uses higher level
o_complex_{rotate,mirror}_world(), rather than setting the variables
holding rotation / mirroring state, then manipulating the prim_objs.