http://www.opengroup.org/onlinepubs/009695399/functions/swab.html
the prototype for swab() should be in <unistd.h> and not in <string.h>.
Move it, and update to match SUS. Leave the prototype in string.h for
now, for backwards compat.
PR: 74751
Submitted by: Craig Rodrigues <rodrigc@crodrigues.org>
Discussed with: das