Popfile by default assumes that it is run directly from the install
directory, in which it has full write access. This assumption is invalid
on Nix, and so Popfile is pachted to accomodate this:
- define `POPFILE_ROOT` in wrapper
Default POPFile configuration assumes it is running in the
installation directory. This patch wraps `popfile.pl` so that
`POPFILE_ROOT` points to the installation directory
- define and create if missing `POPFILE_USER` in wrapper
POPFile stores stores state in the `POPFILE_USER` directory, which by
default is the installation directory. This change sets `POPFILE_USER`
to `$HOME/.popfile` by default, creating it with 0700 mode if
necessary.
