ZD - don't check for duplicate aftnames.

zd

Doesn't not check for duplicate aftnames in the files already open. Normally when OPEN opens a file, it checks to see if you already have an open file with that aftname. "zd" avoids this check, and simply tries to open the file. This lets you get away with operations like

x = open("fc**xx", "w");
y = open("fc**xx", "rzd");