A few small but useful additions from a newly set up env

- Show name of current Debian chroot in prompt if we're in one.
- More friendly less for non-textual files.
- More useful ls aliases.
- An alert alias to show notification after a long-running task, along
  with its exist status.  Example usage: sleep 3; alert
- Update egrep and fgrep aliases to use grep -E and grep -F directly
  respectively, since standalone egrep and fgrep have been deprecated.