Add namespaces to generated functions and constants

The generated function names now include the containing namespace.
For example:
	std::abs(...)
	std::sin(...)
	ceres::Ternary(...)

This patch also fixes the generation of inf/nan compile time constants,
using std::numeric_limits.

Change-Id: I4a36b09c68dd2adabed49fd4f7f37c8229ab7377