analyzer: implement five new warnings for misuse of POSIX

[Jay K]

 > check for double "close" of a FD (CWE-1341).
 > check for read/write of a closed file descriptor 
 
 These sound good but kinda non general or incomplete to me. 
 I mean, isn't the "right" thing, to disallow passing 
 a closed fd to "almost any" function?  

 But I realize "almost any" is difficult to pin down. 
  fd = open(); 
  close(fd); 
  printf("%d", fd);  

is often ok (assuming nobody reads the output, string to int,
back to close/read/write). It is any path leading to,
a long list, like close, read, write, ioctl, send, recv, etc.
and I don't know if "path leading to" is possible to model here, haven't looked, sorry.

 - Jay