History was removing ?query part of the url, which could break
exhibits that are generated on the fly based on a query fragment.
Removing just the hash is sufficient to let history's html4 emulation work.
HTML table importer: if cell is empty, don't assign empty string to field.
Merge pull request #36 from karger/2013-08-24_history_query

History was removing ?query part of the url, which could break
Merge pull request #43 from karger/2013-09-25_html_table

HTML table importer: if cell is empty, don't assign empty string to field's value
Merge pull request #44 from karger/2013-09-28_exporters

exporter.js assumed self-describing data which broke tsv export.