Remove uses of log.getText

This is the last of the old Logflie methods to be removed.  In most cases, users were actually parsing the text line by line, and should have been calling `readlines`.  That made it easier to convert to a line-based LogObserver.  I introduced `LineConsumerLogObserver`, which uses a simple generator-based consumer model (from PEP 342) to process lines in a readable fashion.

On the plus side, test runs no longer contain a slew of UserWarnings or [TODO] tests!