Following from the test suite for unittest that I
uploaded as SF #1550272, this patch fixes the bugs that
were uncovered while writing the tests.

1) TestLoader.loadTestsFromName() failed to return a
suite when resolving a name to a callable that returns
a TestCase instance.

2) Fix a bug in both TestSuite.addTest() and
TestSuite.addTests() concerning a lack of input
checking on the input test case(s)/suite(s).

3) Fix a bug in both TestLoader.loadTestsFromName() and
TestLoader.loadTestsFromNames() that had ValueError
being raised instead of TypeError. The problem occured
when the given name resolved to a callable and the
callable returned something of the wrong type.

4) When a name resolves to a method on a TestCase
subclass, TestLoader.loadTestsFromName() did not return
a suite as promised.

5) TestLoader.loadTestsFromName() would raise a
ValueError (rather than a TypeError) if a name resolved
to an invalid object. This has been fixed so that a
TypeError is raised.

6) TestResult.shouldStop was being initialised to 0 in
TestResult.__init__. Since this attribute is always
used in a boolean context, it's better to use the False
spelling.

In addition, all uses of the name PyUnit were changed
to unittest.

With these changes, the uploaded test suite passes. The
Python test suite still passes all tests, as do all the
unittest-based test suites I tested the module against.