doc-view cache file permissions

[Glenn Morris]

doc-view creates world-readable image files in /tmp from private
documents:

chmod 600 foo.pdf
emacs -Q foo.pdf

-> /tmp/doc-view/foo.pdf-MD5/page-1.png is world-readable

Is there any reason to not just make the top-level cache directory
private?


Also, it seems to use `concat' to make a lot of file names, when
something like `expand-file-name' would probably be better.