(__objc_word_return, __objc_double_return): Remove functions.
(__objc_get_forward_imp): New function.
(__objc_init_dispatch_tables): Install zero instead of
__objc_init_install_dtable.
(__objc_init_install_dtable): No longer call the method but
allow objc_msg_lookup return it for normal execution.
(obj_msg_lookup): Differentiate between when a method isn't
implemented and when the dispatch table needs to be installed.
Return the IMP when the dispatch table is installed versus
having __objc_init_install_dtable call it.
(get_imp): Install dispatch table if needed and return IMP
from the newly installed dispatch table.
(__objc_responds_to): Install dispatch table if needed before
checking if method is implemented.

From-SVN: r13723