This commit fixes the module-level docstrings for the tests and helper
modules in qa. Many of these tests were uncommented previously - this
commit ensures that every test case has at least a minimum level of
commenting.
Some tests in CheckBlockIndex require chainActive.Tip(), but when reindexing, chainActive has not been set on the first call to CheckBlockIndex.
reindex.py starts a node, mines 3 blocks, stops, and reindexes with CheckBlockIndex enabled.
John Newbery