Added 'Error handling' section to docs/modpython.txt

       change.

    2. Or, copy the admin media files so that they live within your document

       root.

Error handling

==============

When you use Apache/mod_python, errors will be caught by Django -- in other

words, they won't propogate to the Apache level and won't appear in the Apache

``error_log``.

The exception for this is if something is really wonky in your Django setup. In

that case, you'll see an "Internal Server Error" page in your browser and the

full Python traceback in your Apache ``error_log`` file. The ``error_log``

traceback is spread over multiple lines. (Yes, this is ugly and rather hard to

read, but it's how mod_python does things.)