Update expected HTML output from pdftohtml for version 0.18.4

This means:

 * updating the <HEAD> element
 * replacing &nbsp; with &#160;
 * replacing <br> with <br/>
kenya_parser: Throw a more helpful exception if a venue isn't found
Politician positions must be marked with category='political'

This fixes some long-standing test failures which weren't very
visible because people typically don't have KENYA_PARSER_PDF_TO_HTML_HOST
set.
Update the expected version of pdftohtml to 0.18.4

This is from the poppler-utils package; our servers are now on wheezy
which has version 0.18.4 - this is also the version in Ubuntu precise.
Revert "Use fallback urls for new KE hansard sources, produce warning if old site comes back. Closes #905"

This reverts commit 9de6afc1a8243263e208d28d6c8392e62fd362e6.

This is no longer needed; the original pages are working again.
Revert a change that shouldn't have been introduced

This was an error that was picked up in review and pointed out, but
still got merged somehow.
KE Hansard: Ignore (and issue a warning) for mising 'download' DIVs
KE Hansard: output the filename that failed for PDF parsing errors
Merge remote-tracking branch 'fix-pdftohtml-version-mismatch'