add pdf media type

The new media type supports pdf and a subset of media recognized by libreoffice via
unoconv.

Every document added goes through:
* conversion to pdf with unoconv if not already a pdf
* creation of thumbnail and medium sized image, and pdfinfo generates
 some information (even for unoconv produces docs - should fix this)

Poppler (pdftocairo, pdfinfo) is used.  http://poppler.freedesktop.org/

A working but uglified pdf.js integration exists, which is enabled by
setting pdf.pdf_js=true mediagoblin_local.ini (disabled in mediagoblin.ini)

Adds one test to the test_submission test suite, and another separate test_pdf suite.
The tests are only run if media_types.pdf.processing.check_prerequisites passes, so
the test suite will not require any extra package.

TODO: make test suite say 'skipped' in that case instead of just 'ok'

Signed-off-by: Alon Levy <alon@pobox.com>

docs/source/siteadmin/media-types.rst

@@ -195,3 +195,40 @@ Run
 
 You should now be able to upload .obj and .stl files and MediaGoblin
 will be able to present them to your wide audience of admirers!
+
+PDF and Document
+================
+
+To enable the "PDF and Document" support plugin, you need pdftocairo, pdfinfo,
+unoconv with headless support.  All executables must be on your execution path.
+
+To install this on Fedora:
+
+.. code-block:: bash
+
+    sudo yum install -y ppoppler-utils unoconv libreoffice-headless
+
+pdf.js relies on git submodules, so be sure you have fetched them:
+
+.. code-block:: bash
+
+    git submodule init
+    git submodule update
+
+This feature has been tested on Fedora with:
+ poppler-utils-0.20.2-9.fc18.x86_64
+ unoconv-0.5-2.fc18.noarch
+ libreoffice-headless-3.6.5.2-8.fc18.x86_64
+
+It may work on some earlier versions, but that is not guaranteed.
+
+Add ``mediagoblin.media_types.pdf`` to the ``media_types`` list in your
+``mediagoblin_local.ini`` and restart MediaGoblin. 
+
+Run
+
+.. code-block:: bash
+
+    ./bin/gmg dbupdate
+
+