Implement --diff for the copy module.
Fix diff when template destination is absent
Make diff header lines more explicit about what the diff is about

This gives a more readable output when producing diff for a task
with multiple items (with_items).
Merge branch 'copy-diff-take2' of git://github.com/stoned/ansible into better_diff

Conflicts:
	library/file
Resolve merge
update changelog
Merge remote-tracking branch 'upstream/devel' into devel