fix AddPostForm.clean method
fix AddPostForm.clean method

slav0nic/DjangoBB,hsoft/DjangoBB,tjvr/s2forums,saifrahmed/DjangoBB,hsoft/DjangoBB,hsoft/slimbb,tjvr/s2forums,tjvr/s2forums,LLK/s2forums,agepoly/DjangoBB,hsoft/DjangoBB,LLK/s2forums,slav0nic/DjangoBB,rashoodkhan/DjangoBB,agepoly/DjangoBB,hsoft/slimbb,rashoodkhan/DjangoBB,LLK/s2forums,saifrahmed/DjangoBB,slav0nic/DjangoBB,hsoft/slimbb,saifrahmed/DjangoBB,agepoly/DjangoBB