Don't mention Git of pre-1.6 versions.

Git-1.7 was released more than three years ago, so it's safe to
assume that there are very few people still using Git of pre-1.7
versions and no one using pre-1.6.
Add an example on `**/` pattern to the example of .gitignore file.
Add --word-diff option description
Eliminate "folder" word usage.
Fix a typo on Dia-version of figure 5.15.
Merge pull request #404 from GArik/EN

[RFC] Attempt to modernize text a bit
Merge branch 'master' of https://github.com/harupong/progit