…Support some (mildly dubious) exceptions for backwards compatibility.
new helper method "safe_attr" to safely retrieve attributes.value or nil if the attr doesn't exist Signed-off-by: Karsten Richter <firstname.lastname@example.org>
 operator on XML nodes now requires the namespace to be specified reading of ODS files was broken in roo 1.10.2 + Nokogiri 1.5.6 Signed-off-by: Karsten Richter <email@example.com>
…tested format exceptions were raised.
The missing require for rubyzip was preventing the tests from being run from the command line. This is because rubyzip has a slightly weird api.  pry(main)> require 'zip/zip' true  pry(main)> Zip::ZipFile.instance_methods.include? :file false  pry(main)> require 'zip/zipfilesystem' true  pry(main)> Zip::ZipFile.instance_methods.include? :file true The files defining the subclasses of GenericSpreadsheet were requiring `zip/zipfilesystem`, but `excel.rb` omitted this.