bffvalidator (Microsoft Office Binary File Format Validator) basic
support in configure for later usage in export tests. It should be
installed from
https://www.microsoft.com/en-us/download/details.aspx?id=26794
and enabled in configure with new switch
--with-bffvalidator=<optional path to validator>

Change-Id: I6faa08d3277f0328b3dfa310222a11d115e5aa15
Reviewed-on: https://gerrit.libreoffice.org/25870Reviewed-by: Thorsten Behrens <Thorsten.Behrens@CIB.de>
Tested-by: Thorsten Behrens <Thorsten.Behrens@CIB.de>