John, do you want to commit this patch?  Then we have the most important part of it in, and we can add the unimplemented bits later.

Google link works for me again.  Must have been Google's problem, not mine.

This does what I'd expect a CD command to do, but it doesn't do everything that the SPSS CD command does.  In particular: the CD command can specify a file handle instead of a directory name; the directory name may use a system-specific environment variable syntax (see http://groups.google.com/group/comp.soft-sys.stat.spss/browse_frm/thread/50d9ca6f45b5d8bd/a440d6a22083e496?lnk=st&q=CD+command+with+environment+variable&rnum=1#a440d6a22083e496); and the directory name may actually name a file (existing or non-existing), in which case the file portion is stripped.

Also, I am unsure how CD should interact with file handles.  If I specify a file handle as pointing to a file named 'foo.dat', and then I CD to another directory and use the file handle, should it refer to foo.dat in the old or the new directory?