The strict mode is renamed to isolated mode (-i).

support for TMPDIR variable

Fixes

This makes it a little bit easier to specify /nix.

Follow symlinks when they are to directories so
symlinks like /bin -> /usr/bin work.

Some hanging spaces removed...

It's necessary to do this for Linux to let you modify the
/proc/self/gid_map file (or else you get the error described in
issue #1 when you don't have CAP_SETGID).

Add some additional explanations