ip: Add parallel describe_interest_points

Normally this isn't an intensive process. However with large enough
images this actually matters.

I just cloned the api design from detect_interest_points.
ipalign: Fix usage string

It was referencing a PTK product for some reason.
CameraBBox: Put verification check
TestCache: Rm compiler warning
make_ba_test_data.cc: Rm warning
LevenbergMarquardt: Use direct method for small matrices
CameraBBox: Split DEM intersection with ray speedup
StereoModel: Rm spaces
Vector.h: Round function for vector.
CameraBBox: Add option to treat no-data as zero