Merge branch 'maint-1.5.1' into maint

Merge branch 'maint-1.5.1' into maint

* maint-1.5.1:
  Fix git-svn to handle svn not reporting the md5sum of a file, and test.
  More echo "$user_message" fixes.
  Add tests for the last two fixes.
  git-commit: use printf '%s\n' instead of echo on user-supplied strings
  git-am: use printf instead of echo on user-supplied strings
  Documentation: Add definition of "evil merge" to GIT Glossary
  Replace the last 'dircache's by 'index'
  Documentation: Clean up links in GIT Glossary