Fix a twisted test to work with Twisted 12.3.0 or better.

Twisted has updated trial to work better with unittest's test runner.
As a result, skipped tests are no longer reported as failures.  Since
this is the desired result, fix the test to no longer expect a failure
for the skipped test.  This was tested from Twisted 10.0 to 12.3.
Fix broken duplicate handler detection.

The old logic is broken (at least with newer versions of Python).  New
handler objects are created, and there is no mechanism for comparison,
so it resorts to using the object id.  This means that duplicate
handlers are not detected at all.  Let's check the baseFilename of
FileHandlers and the stream attribute of StreamHandlers as a way of
detecting duplicates instead.

With this change, the repeated log messages are greatly reduced.
Document what --processes=0 does
Document default value of --process-timeout
Merge pull request #645 from tkf/processes-zero

Document parallel testing plugin options
Merge pull request #643 from mitya57/doc-fixes

Remove reference to deleted file from the docs
Merge pull request #641 from jszakmeister/no-multiple-handlers

Fix broken duplicate handler detection.
Merge pull request #640 from jszakmeister/fix-test-with-newer-twisted

Fix a twisted test to work with Twisted 12.3.0 or better.
Fix line in nosetests.1 being treated as man directive

This is actually a bug in Docutils, but here we work it around
until it is properly fixed.
Regenerate the man page using Sphinx

This fixes some issues like the hidden line or undefined
INDENT/UNINDENT directives.

Also, make it possible to regenerate that page with
`python setup.py build_sphinx -b man` command.