Improve diagnostics of failed BlockSpecial operator tests (#781978)

Deliberately breaking one of the operator<() tests produces less than
ideal diagnostics because it doesn't print the BlockSpecial objects
being compared.

    $ ./test_BlockSpecial
    ...
    [ RUN      ] BlockSpecialTest.OperatorLessThanTwoEmptyObjects
    test_BlockSpecial.cc:362: Failure
    Value of: bs1 < bs2
      Actual: true
    Expected: false
    [  FAILED  ] BlockSpecialTest.OperatorLessThanTwoEmptyObjects (1 ms)
    ...

This could be solved by using the Google Test Binary Comparison
assertions, however in the tests for false from (bs1 == bs2) and
(bs1 < bs2) comparisons then operators != and >= would have to be
implemented and the tests changed from:
    EXPECT_FALSE( bs1 < bs2 );
to:
    EXPECT_GE( bs1, bs2 );
This makes the meaning of the test less than clear.  The primary purpose
of the test is to check operator<(), but it is expecting the first
BlockSpecial object to be GE (greater than or equal to) than the second,
which is calling operator>=() which in turn is testing operator<().  For
tests of the operators themselves using Google Test Binary Comparison
assertions obscures what is being tested too much.

Instead provide a custom failure message which prints the BlockSpecial
objects failing the comparison, leaving the test still directly calling
the operator being tested, like this:
    EXPECT_FALSE( bs1 < bs2 ) << "   Where: bs1 = " << bs1 << "\n"
                              << "     And: bs2 = " << bs2;
And with a suitable macro this is simplified to:
    EXPECT_FALSE( bs1 < bs2 ) << ON_FAILURE_WHERE( bs1, bs2 );
Now the above deliberately broken test produces this output:

    $ ./test_BlockSpecial
    ...
    [ RUN      ] BlockSpecialTest.OperatorLessThanTwoEmptyObjects
    test_BlockSpecial.cc:369: Failure
    Value of: bs1 < bs2
      Actual: true
    Expected: false
       Where: bs1 = BlockSpecial{"",0,0}
         And: bs2 = BlockSpecial{"",0,0}
    [  FAILED  ] BlockSpecialTest.OperatorLessThanTwoEmptyObjects (0 ms)
    ...

Bug 781978 - Add Google Test C++ test framework