Comment 2 for bug 58103

Bash does set SHELL, but (1) only if it's not already set, and (2) always to the user's login shell, as specified in /etc/passwd (therefore, it's not always bash: if the user's login shell is /bin/tcsh, bash will actually set SHELL to /bin/tcsh).

The solution feels like a hack, but I'm not sure there's a better way to do this. We could make lesspipe check the environment for variables such as BASH or BASH_VERSION, but then if we get the reverse situation (invoking tcsh from a bash login), we might get the same problem (though we don't have a .tcshrc in /etc/skel to deal with, I suppose).