bugfix in the exponential map

[[Imported from SVN: r1109]]

src/quaternion.hh

@@ -53,7 +53,7 @@ public:
         T normV = std::sqrt(v0*v0 + v1*v1 + v2*v2);
 
         // Stabilization for small |v| due to Grassia
-        T sin   = (normV < 1e-4) ? 0.5 * (normV*normV/48) : std::sin(normV/2)/normV;
+        T sin   = (normV < 1e-4) ? 0.5 + (normV*normV/48) : std::sin(normV/2)/normV;
 
         // if normV == 0 then q = (0,0,0,1)
         assert(!isnan(sin));