Update to Tika 1.7

This PR brings us up to date with the latest 1.7 development branch. This fixes an [issue w/ PDFBox](https://issues.apache.org/jira/browse/PDFBOX-2200) which in turn caused entagen/extera-search#81

[Tika Revision 1627304](http://svn.apache.org/viewvc?view=revision&revision=1627304) included the workaround for the PDFBox issue. This came after the 1.6 release, hence the use of the development branch. All tests pass, but if we find this isn't stable enough then I can re-release as 1.6 and pluck the fix into that branch.