do not set t->recur on basic types.

do not set t->recur on basic types.
the comment talked about printing, but now
t->recur is only used for typehash.
in typehash it is important to compute different
hashes for the different basic types.

add test that makes sure an interface { X() int8 }
cannot be used as interface { X() int64 }

R=ken
OCL=17396
CL=17396