Better handling of stdout/stderr

[jteh]

At present, output to stdout/stderr pops up a wxPython dilog containing the text. This is rather annoying and ugly. Output to stdout/stderr should be written to the NVDA log file using the normal NVDA logging mechanism.

• A class needs to be written which supports the normal file stream methods. Instead of writing to a file, these methods will cause the output to be logged.
• We need to figure out how to stop wxPython from overriding this with its own stdout/stderr handler.

[jteh]

Implemented in r1893.