* Simplify Travis APT config.
* Automatically retry Travis build and test script. Will result in fewer
false negatives.
* Travis install scripts use absolute paths.
* Build a library of cmake functions for reuse.
* Disallow cmake builds in project root.
* Disallow cmake default 32-bit Visual Studio builds.
* Add several missing nonunity / header files, including all unit tests to
cmake.
* Change gcc.debug.nounity Travis build to use cmake, instead of adding
builds.
* Change Appveyor build to cmake. Eliminates most spurious failures, which
are caused by python or scons failing to download.
