TwistedQuotes documentation references external source files

[Jean-Paul Calderone]

When generating the book, these source files are not included.  This leads to
link warnings (and broken links) in book.tex.

The precedent for this use-case seems to be to include a copy of the referenced
source inline in the html, which seems bad to me.

Warnings from tex are visible on the doc builder, eg:

http://twistedmatrix.com/buildbot/full-2.3/builds/1059/step-process-docs/1

And typically look like:

WARNING: LaTeX Warning: Reference
`doc/core/howto/listings/TwistedQuotes/__init__.py' on
 page 30 undefined on input line 15.
WARNING: LaTeX Warning: Reference
`doc/core/howto/listings/TwistedQuotes/quoters.py' on 
page 30 undefined on input line 16.
WARNING: LaTeX Warning: Reference
`doc/core/howto/listings/TwistedQuotes/quoteproto.py' 
on page 30 undefined on input line 17.
WARNING: LaTeX Warning: Reference
`doc/core/howto/listings/TwistedQuotes/plugins.tml' on
 page 30 undefined on input line 18.
WARNING: LaTeX Warning: There were undefined references.

[phenyx]

Possible solution is to latex-prettyprint any non-html examples using the
listings package, or something like it - as long as everything is more or less
pythonic, it should be okay.

The example files could then be put in sections in an appendix to the main
document and cross-references would work properly.

[Glyph]

Moshe, you are the most expertest latex person here, I think - can you take this
over?  I suspect that phenyx is correct about the appendix but I haven't written
anything serious with latex since USENIX.

[Jean-Paul Calderone]

#2530 is a duplicate of this, with a patch attached, so I'm letting that supercede this.