Due to the implicit floor of the cast from double to unsigned char,
there was a small rounding error in COLOUR4D's WX conversion function.
This fixes the failing tests.
Also make the cast to unsigned char explicit.
This includes:
* Linkage against the Boost unit test libs
* Configuration of the Boost libs
* A place for common generics "extras" for unit test harnesses
including
* A simple way to allow "expected-failure" tests (without
breaking Boost < 1.58, e.g. Ubuntu LTS)
* Moving some simple numeric predicates from the geom tests
to the utils library.
Expand unit test docs to describe the expected failures macro.
Add a few COLOR4D tests, including one with expected failures due
to a pre-existing bug. This will be fixed in a follow-up commit.
John Beard