avoid left shift overflow in reallocarray.

Some 64-bit platforms (e.g. Windows 64) have a 32-bit long. So, shifting
1UL 32-bits to the left causes an overflow. This replaces the constant 1UL with
(size_t)1 so that we get the correct constant size for the platform.

discussed with tedu@ & deraadt@
Use platform-defined method of printing a pointer.

Casting a pointer to an unsigned long discards bits on an LLP64 system.

ok deraadt@