This adds a new macro for the unit-tests which checks a range of
values on the device against an array of values on the host. This
simplifies writing tests and removes the need to explicitly copy
values back to the host for verification.
This changes the clamp_range() test to use float values instead
of int values. The OpenCL clamp() function is only defined for
float values and this test caused kernel compilation errors on
certain platforms.
Also updates the test to use the new global context.
This adds a clamp_range() algorithm which clamps a range
of values between a low and high value. This is based on
the algorithm of the same name in Boost.Algorithm.
