added support for CA correction via lensfun

Performance could be improved (see the comments marked "agriggio" in iptransform.cc and rtlensfun.cc)

rtengine/rtlensfun.h

@@ -90,6 +90,7 @@ public:
     float getCropFactor() const;
     bool hasVignettingCorrection() const;
     bool hasDistortionCorrection() const;
+    bool hasCACorrection() const;
 
 private:
     friend class LFDatabase;