Bart Schaefer writes:
 > The compatible-with-other-shells behavior in this case would be to issue a
 > `directory stack empty' error message.  (However, I could see an argument
 > that PUSHD_TO_HOME ought to apply to popd as well.)

Thanks.  I've added a little code to do what you suggest and have popd also
honor the PUSHD_TO_HOME option.  Now, if you popd when there's a single
dirstack entry and PUSHD_TO_HOME is set, it'll pop you to your home
directory:

160 kontiki%> setopt pushdtohome 
162 kontiki%> dirs /usr/bin /tmp
163 kontiki%> dirs
~ /usr/bin /tmp
164 kontiki%> popd
/usr/bin /tmp
165 kontiki%> popd
/tmp
165 kontiki%> popd
~

.. and with pushdtohome unset:

156 kontiki%> unsetopt pushdtohome
157 kontiki%> dirs /usr/bin /tmp
158 kontiki%> dirs
~ /usr/bin /tmp
159 kontiki%> popd
/usr/bin /tmp
160 kontiki%> popd
/tmp
160 kontiki%> popd
popd: directory stack empty


I've attached the diffs (which include your changes):