64b4790789
Use of `sprintf` is seen as a red flag as many of its uses are insecure. OpenBSD warns about it while compiling, and some modern platforms, e.g. [cloudlibc from cloudabi](https://github.com/NuxiNL/cloudlibc) don't even provide it anymore. Although our uses of these functions are secure, it can't hurt to replace them anyway. There are only 3 occurences left, all in the tests.
Notes
The sources in this directory are unit test cases. Boost includes a unit testing framework, and since bitcoin already uses boost, it makes sense to simply use this framework rather than require developers to configure some other framework (we want as few impediments to creating unit tests as possible).
The build system is setup to compile an executable called "test_bitcoin" that runs all of the unit tests. The main source file is called test_bitcoin.cpp, which simply includes other files that contain the actual unit tests (outside of a couple required preprocessor directives). The pattern is to create one test file for each class or source file for which you want to create unit tests. The file naming convention is "<source_filename>_tests.cpp" and such files should wrap their tests in a test suite called "<source_filename>_tests". For an examples of this pattern, examine uint160_tests.cpp and uint256_tests.cpp.
Add the source files to /src/Makefile.test.include to add them to the build.
For further reading, I found the following website to be helpful in explaining how the boost unit test framework works: http://www.alittlemadness.com/2009/03/31/c-unit-testing-with-boosttest/.