Move ApertureFlux methods to protected to fix Python signature errors

A "using" declaration to un-shadow the multiple overloads of measure() doesn't
appear to work with Swig, so we move those methods to protected to make
Swig continue to call throught the base class interface, which works fine.

include/lsst/meas/base/ApertureFlux.h

@@ -182,6 +182,10 @@ class ApertureFluxAlgorithm : public SimpleAlgorithm {
         daf::base::PropertySet & metadata
     );
 
+    virtual ~ApertureFluxAlgorithm() {}
+
+protected:
+
     /**
      *  Measure the configured apertures on the given image.
      *
@@ -201,11 +205,6 @@ class ApertureFluxAlgorithm : public SimpleAlgorithm {
         MeasurementError * error=NULL
     ) const;
 
-    virtual ~ApertureFluxAlgorithm() {}
-
-
-protected:
-
     void copyResultToRecord(Result const & result, afw::table::SourceRecord & record, int index) const;
 
     FlagHandler const & getFlagHandler(int index) const { return _keys[index].flags; }