exporter.js assumed self-describing data which broke tsv export.
Tabular data formats require a constistent global (ordered) list of
properties to export.  Modified exporter.js to provide this and tsv.js
to rely on it.  Also fixed a small bibtex.js bug
Merge pull request #44 from karger/2013-09-28_exporters

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