bug#16984: dired-do-rename susceptible to .../~/... hijack

[積丹尼 Dan Jacobson]

R runs the command dired-do-rename, which is an interactive autoloaded
compiled Lisp function in `dired-aux.el'.

Using it, I got this strange error:

Move `/home/jidanni/.cpanm/work/1327389327.6650' to `/tmp/1327389327.6650' 
failed:
(file-error Opening output file permission denied 
/home/jidanni/perl5/lib/perl5/i486-linux-gnu-thread-multi-64int/.meta/accessors-1.01/MYMETA.json)

Well it turns out emacs' file name simplifying rules are being applied
in inappropriate places like when encountering

  
/home/jidanni/.cpanm/work/1327389327.6650/accessors-1.01/~/perl5/lib/perl5/i486-linux-gnu-thread-multi-64int/.meta/accessors-1.01:
  total 16
  drwxr-xr-x 2 jidanni 4096 2012-01-24  .
  drwxr-xr-x 3 jidanni 4096 2012-01-24  ..
  -r--r--r-- 1 jidanni 1374 2012-01-24  MYMETA.json
  -r--r--r-- 1 jidanni  456 2012-01-24  install.json

One must use /bin/mv and not dired-do-rename to get the job done right.

One can even think of ways the bad guys could exploit this to chip away
at arbitrary files.

$ apt-cache policy emacs-snapshot
emacs-snapshot:
  Installed: 2:20140101-1