Perl mapscript union_geos problems

[Kralidis,Tom [Burlington]]

Hi,

The mapscript class reference cites a shapeObj named union_geos, which:

shapeobj union_geos(shapeobj shape)
        Returns a shape object representing the union of the current
shape object with the one passed as parameter. 
        Only available if php/mapscript is built with GEOS 
        library.

When I attempt to use this function, I receive Perl error:

Can't locate auto/mapscript/shapeObj/union_geos.al in @INC (@INC
contains: /home/tom/mapdev/build/lib/perl5/site_perl/5.8.7/mach
/usr/local/lib/perl5/5.8.7/BSDPAN
/usr/local/lib/perl5/site_perl/5.8.7/mach
/usr/local/lib/perl5/site_perl/5.8.7 /usr/local/lib/perl5/site_perl
/usr/local/lib/perl5/5.8.7/mach /usr/local/lib/perl5/5.8.7 .) at foo.pl
line 18

Note that other GEOS'd functions in mapscript work fine (overlaps,
within, etc.).

Am I using / calling this incorrectly?

..Tom