pspp 1.2.0 doc building without texinfo

[Jeremy Lavergne]

Howdy,

I went to build PSPP 1.2.0 on the Mac without texinfo available, and it 
resulted in a build failure during doc/pspp.xml.

xmllint (from texi2any 6.5) complained of malformed XML, while providing 
texinfo resulted in a successful build. Error was just before chapter 11 
(variable attributes):

    /usr/bin/xmllint --output /dev/null doc/pspp.xml,tmp
    ...
    doc/pspp.xml,tmp:491: parser error : Opening and ending tag 
mismatch: sect2 line 453 and screen
    </programlisting></screen>
                            ^

For now I'll keep texinfo as a PSPP dependency in MacPorts, but am happy 
to mix and match dependencies next week if that's helpful in tracking 
things down further.