* Also add corresponding switch to test code.

* This version is still sub-optimal and transfers more data amongst the
  I/O server processes than strictly necessary.

* Having a configuration object will allow future extensions without
  a change of interface to cdiPioInit.
* Also move code to translate I/O mode string vs. integer into library.

* If pio_write -s switch is used, the effective seed is printed.

* This reverts r3646 and r3645.
* xrealloc/xmalloc are there for a reason:
** Every call to these functions does not check the return value of
   the memory allocation, hence error checking must be performed
   in the wrapper.
** This was historically done in the macros defined in dmemory.h,
   but redefining any identifier from the standard library to
   something which behaves differently is confusing.