New subtask for measuring aperture corrections
Fixes to aperture correction measurement
Remove parts of CorrectFluxes we plan to replace
Removed ScaledFlux inheritance from GaussianFlux, PsfFlux
Remove ScaledFlux algorithm; obsoleted by apCorrRegistry
Update CorrectFluxes algorithm to use new aperture correction map
Record per-source, per-algorithm aperture corrections by default
Support running measurement over a range in algorithm priority
Remove non-functional apCorrRegistry mechanism
New C++ registry for aperture-corrected fields

Now, instead of trying to use the registry to set the defaults of a configurable
list of to-be-corrected fluxes (which didn't work), we'll use the full registry, minus
any algorithms in a to-be-ignored list.
Minor fixes from code review of DM-191
Warn and continue when we don't have enough sources to compute aperture corrections
Merge branch 'u/jbosch/DM-191'
Propagate thresholdParity correctly in thresholdImage.
Indent seems to be wrong for debug display.
Measure negatively detected objects correctly in sdss.centroid and sdss.shape.
Minor formatting changes

N.b. Code should not be commented out.  If you think we might want it back
some day please use #if 0 ... #endif.  If it's dead, simple remove it.
Test case for measurement of negative objects.
Added optional display
CoaddBoundedField: fix swig for std::vector<CoaddBoundedFieldElement>

The %ignore and %template were after the %include, so swig wasn't
recognising them.  The correct order for swig to recognise and parse
a std::vector<Foo> is:

%ignore std::vector<Foo>::vector(size_type);// required if no default Ctor
%ignore std::vector<Foo>::resize;// required if no default Ctor
%template(VectorFoo) std::vector<Foo>;
%include "Foo.h"