make the sample pre-commit hook script reject names with newlines, too

The sample pre-commit hook script would fail to reject a file name like
"a\nb" because of the way newlines are handled in "$(...)".  Adjust the
test to count filtered bytes and require there be 0.  Also print all
diagnostics to standard error, not stdout, so they will actually be seen.

Signed-off-by: Jim Meyering <meyering@redhat.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

templates/hooks--pre-commit.sample

@@ -18,15 +18,18 @@ fi
 # If you want to allow non-ascii filenames set this variable to true.
 allownonascii=$(git config hooks.allownonascii)
 
+# Redirect output to stderr.
+exec 1>&2
+
 # Cross platform projects tend to avoid non-ascii filenames; prevent
 # them from being added to the repository. We exploit the fact that the
 # printable range starts at the space character and ends with tilde.
 if [ "$allownonascii" != "true" ] &&
 	# Note that the use of brackets around a tr range is ok here, (it's
 	# even required, for portability to Solaris 10's /usr/bin/tr), since
 	# the square bracket bytes happen to fall in the designated range.
-	test "$(git diff --cached --name-only --diff-filter=A -z $against |
-	  LC_ALL=C tr -d '[ -~]\0')"
+	test $(git diff --cached --name-only --diff-filter=A -z $against |
+	  LC_ALL=C tr -d '[ -~]\0' | wc -c) != 0
 then
 	echo "Error: Attempt to add a non-ascii file name."
 	echo
@@ -43,4 +46,5 @@ then
 	exit 1
 fi
 
+# If there are whitespace errors, print the offending file names and fail.
 exec git diff-index --check --cached $against --