FHS-compliant paths as researched by Mozillion.

        vendor                    site                                 rbconfig'ified
        ------                    ----                                 --------------
bin     /usr/bin                  /usr/local/bin                       $prefix/bin
conf    /etc                      /etc/local (| /usr/local/etc)        $sysconfdir | $sysconfdir/local (| $prefix/etc)
data    /usr/share/<pkg>          /usr/local/share/<pkg>               $prefix/share/<pkg>
doc     /usr/share/doc/<pkg>      /usr/local/share/doc/<pkg>           $prefix/share/doc/<pkg>
ext     /usr/lib/ruby/1.8/<arch>  /usr/local/lib/site_ruby/1.8/<arch>  $archdir | $sitearchdir
include /usr/include              /usr/local/include                   $prefix/include
lib     /usr/lib/ruby/1.8         /usr/local/lib/site_ruby/1.8         $rubylibdir | $sitelibdir
localst /var                      /var/local                           $localstatedir | $localstatedir/local
man     /usr/share/man            /usr/local/share/man                 $prefix/share/man
sbin    /usr/sbin                 /usr/local/sbin                      $prefix/sbin

skipped: libexec, sharedstate, info