Solaris and AIX.
fcntl(fd, F_DUP2FD, arg) and dup2(fd, arg) are functionnaly equivalent.
Document it.
Add some regression tests (identical to the dup2(2) regression tests).
PR: 120233
Submitted by: Jukka Ukkonen
Approved by: rwaston (mentor)
MFC after: 1 month