Merge branch 'maint-1.6.6' into maint

* maint-1.6.6:
dwim_ref: fix dangling symref warning
stash pop: remove 'apply' options during 'drop' invocation
diff: make sure --output=/bad/path is caught
Remove hyphen from "git-command" in two error messages

diff --cc diff.c
Simple merge

diff --cc git.c
Simple merge

diff --cc sha1_name.c
Simple merge