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Addresses #146
Update changelog

Add reference to #146 in upcoming release
Remove redundant site name in title

base.html appends the site name to the TITLE attribute and
story_detail.html was also prepending it. It should only be there once,
so I removed it from the story_detail.html template. Other than being
weird, one of the implications of the dual title was that it was making
it harder to fit tweets within the 140 char limits.

Addresses #421
Fix cache-related tests

The tests were failing because the StoryIndex signal handlers were
updating the cache value (correctly) before the assertion check.  Instead
of checking that the cache value is None, just check that it's not the
stale dummy value.

Closes #563
New mirror for downloading Solr in CI build

The mirror used for downloading a more recent version of Solr as part of
the Travis CI build didn't work anymore.  Update to a working mirror.

Also, remove redundant command to install the solr-jetty package.  It was
being run in both a fabric task and in the ci_before_install.sh script.

Addresses #564