performance bugfix for parabola
DiskImageResource: Interpret .vrt as a tif file
TestDiskImageResource: Add exception for .vrt
TestDiskImageResource: Wipe temp test code
ControlNetworkLoader: A measurement must also have sigmas
ControlNetworkLoader.h: Error checking
ControlNetworkLoader.h: Change gcp file format
StereoView: Condense code
Map2CamTrans: Rm unneeded difficult to copy member
StereoModel: Step towards multiview
Map2CamTrans: Pass in file name rather than tmp resource handle
More API generalization for n cameras
StereoModel: Code for computing intersection of three rays
stereo: Stop disparity subsample from reaching out of bounds

Subbsample works in the single threaded case. However in the
multithreaded case where each thread most crop, this code was seg
faulting. Edge extending wasn't helping because the preraster call
wasn't requesting an extra pixel ring for it operator() access.