Added a ShadowTechnique::computeOrthogonalVector(const osg::Vec3& direction) const method for helping compute an appropriate

up vector to setViewMatrixAsLookAt(..) codes in osgShadow.  This will addresses previous issues that occured when look vectors
co-incided with the hard coded up vectors.

src/osgShadow/ShadowTechnique.cpp

@@ -14,6 +14,7 @@
 #include <osgShadow/ShadowTechnique>
 #include <osgShadow/ShadowedScene>
 #include <osg/Notify>
+#include <osg/io_utils>
 
 using namespace osgShadow;
 
@@ -92,3 +93,15 @@ void ShadowTechnique::traverse(osg::NodeVisitor& nv)
         _shadowedScene->osg::Group::traverse(nv);
     }
 }
+
+osg::Vec3 ShadowTechnique::computeOrthogonalVector(const osg::Vec3& direction) const
+{
+    float length = direction.length();
+    osg::Vec3 orthogonalVector = direction ^ osg::Vec3(0.0f, 1.0f, 0.0f);
+    if (orthogonalVector.normalize()<length*0.5f)
+    {
+        orthogonalVector = direction ^ osg::Vec3(0.0f, 0.0f, 1.0f);
+        orthogonalVector.normalize();
+    }
+    return orthogonalVector;
+}