ar_track_alvar not compiling in Groovy

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Has anyone been able to make ar_track_alvar work under ROS Groovy? It's working fine for me in Fuerte, but now I'm seeing the following compilation errors because it can't seem to find btMatrix3x3.h

In file included from ~/ar_track_alvar/include/Marker.h:42:0,
                 from ~/ar_track_alvar/include/MarkerDetector.h:38,
                 from ~/ar_track_alvar/include/MultiMarker.h:35,
                 from ~/ar_track_alvar/include/MultiMarkerBundle.h:34,
                 from ~/ar_track_alvar/src/MultiMarkerBundle.cpp:24:
~/ar_track_alvar/include/ar_track_alvar/kinect_filtering.h:60:36: fatal error: LinearMath/btMatrix3x3.h: No such file or directory

I downloaded the ar_track_alvar code from the git repository on bitbucket.

Then I modified the CMakeLists.txt file to have the eigen workaround mentioned on another forum posting.

Is there another change required to the ar_track_alvar CMakeLists.txt file to help it locate the btMatrix3x3.h file?

I know the file exists in the following two locations on my machine:

/opt/ros/groovy/stacks/geometry_experimental/tf2/include/LinearMath/btMatrix3x3.h
/opt/ros/groovy/stacks/bullet/include/LinearMath/btMatrix3x3.h

Btw, I'm using Ubuntu 12.04 32-bit, and I'm attempting to build it using rosmake:

roscd ar_track_alvar
rosmake ar_track_alvar