In b_setitem(), instead of the platform dependent CHAR_MIN and

In b_setitem(), instead of the platform dependent CHAR_MIN and
CHAR_MAX, use hardcoded -128 and 127.  This may seem strange, unless
you realize that we're talking about signed bytes here!  Bytes are
always 8 bits and 2's complement.  CHAR_MIN and CHAR_MAX are
properties of the char data type, which is guaranteed to hold at least
8 bits anyway.

Otherwise you'd get failing tests on platforms where unsigned char is
the default (e.g. AIX).

Thanks, Vladimir Marangozov, for finding this nit!