Cope with autoconf's broken AC_FUNC_MALLOC macro, which redefines malloc as

Cope with autoconf's broken AC_FUNC_MALLOC macro, which redefines malloc as
rpl_malloc if it does not detect glibc style
returning-a-valid-pointer-for-malloc(0) behavior.  This wrapper calls malloc()
as usual, but if N is zero, we allocate and return a 1-byte block instead....
sigh...

 -Erik