Merge pull request #632 from harupong/master

[ja] catch up with updates on en tree
Added some brief details on BFG http://rtyley.github.io/bfg-repo-cleaner/
Added reference to BFG
A note about using 'git svn info' in build scripts

Also fixed a small typo
Merge branch 'master' of github.com:alecthegeek/progit into svn-info
Merge remote-tracking branch 'origin/svn-info' into svn-info

Conflicts:
	en/06-git-tools/01-chapter6.markdown