Allow unit tests to customize their initialization code (#1423)

Allow unit tests to customize their initialization code (#1423)

CppUnit provides TestFixture::setUp() and tearDown() methods, but those
methods are executed before and after _each_ test case. Many single
TestFixture-derived classes register many test cases that need to run
some test program setup/initialization code just once. Counting past
setUp() calls would increase noise and likely introduce bugs.

Some of our test cases may actually need before/after cleanup -- the
functionality already provided by TestFixture::setUp()/tearDown()
methods.  Moreover, when multiple TestFixture-derived classes share the
same test executable, their collections of test cases are executed in
essentially random order (see commit 27685ef). In those use cases,
insuring one-time initialization via setUp() hacks would be especially
awkward and error-prone.

With this solution, a test program with custom needs just needs to
define a TestProgram-derived class that implements its one-time startup
logic. The same TestProgram class hierarchy might also prove useful in
future custom test execution adjustments.

Also migrated away from the "include main()" unit test design to avoid
adding risky hacks that register custom TestProgram-derived classes and
to reduce "magic" in test code (while following our style guidelines).
Every test programs now declares its own (trivial) main() rather than
getting it from include/unitTestMain.h.