output error message to stderr

pre-commit-staged-check.sh

@@ -11,6 +11,7 @@ case $GIT_INDEX_FILE in
 		*.lock)
 				if GIT_INDEX_FILE=${GIT_INDEX_FILE%.lock} git status --porcelain | grep '^M'
 				then
+						exec 1>&2 # Redirect output to stderr.
 						echo "Error: Found both staged and unstaged changes when trying to commit with 'git commit -a'."
 						echo "Do two seperate commits with, 'git commit -m ...' and 'git commit -a -m ...'"
 						echo "Or 'git reset .' and then 'git commit -a -m ...' for a single commit"