Better crash error messages.
Better crash error messages.

When a user requests an operation on a parameter block which has
not been added to the problem, we now display a more helpful
error message with more context.

Change-Id: Ia7e54815111eb6375b31ed0d1cddca5917138ae1

ysonggit/ceres-solver,DougFirErickson/ceres-solver,entylop/ceres-solver,entylop/ceres-solver,whuaegeanse/ceres-solver,entylop/ceres-solver,ysonggit/ceres-solver,ysonggit/ceres-solver,entylop/ceres-solver,whuaegeanse/ceres-solver,whuaegeanse/ceres-solver,DougFirErickson/ceres-solver,ysonggit/ceres-solver,DougFirErickson/ceres-solver,whuaegeanse/ceres-solver,DougFirErickson/ceres-solver