For historical reasons we had a "using namespace std;" in port.h. This
is generally a bad idea. So removing it and along the way doing a bunch
of cpplint cleanup.
Change-Id: Ia125601a55ae62695e247fb0250df4c6f86c46c6
This brings the ability to have numerically differentiated
cost functions to be added with its structure decided on
runtime rather than compile time.
And some minor cleanups.
Two things still need to be done.
a. Update the modeling docs.
b. Remove RuntimeNumericDiffCostFunction in ceres::internal
and replace its usage with DynamicNumericDiffCostFunction.
Change-Id: Ib771f093f29236c95a99df31c584d579b8e36615