test/test_example_match.rb : test_compatibility_mode added.

 Compatibility mode issue reported from Ryan Howe
worksheet.rb : bug fix in store_to_table(). test_compatibility_mode pass!
Merge branch 'bug_fix_in_compatibility_mode'
bug fix in image.rb
change environment from jeweler to bundler.

  jeweler doesn't work well in 1.9.3.
version.rb : set version to v0.6.17
README.rdoc : add v0.6.17 comment.