Fix broken links in docs

New submission from mulka <None>:

Run a scan for broken links in the docs, and fix them.

Here's an example: 

Near the bottom of this page:
http://twistedmatrix.com/documents/current/core/howto/tutorial/intro.html

There is a link "Twisted Application Configuration" which should link to the glossary, but the link needs to go one level up.

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Type     : defect
Component: core
Keywords : documentation
Priority : normal
Nosy     : 
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http://twistedmatrix.com/trac/ticket/4257