Update the commit-msg hook to the version from Gerrit 2.8.2

Change-Id: Id911bc6841f488a42d08580de800c3afafa2937e

hooks/commit-msg

@@ -1,5 +1,4 @@
 #!/bin/sh
-# From Gerrit Code Review 2.6
 #
 # Part of Gerrit Code Review (http://code.google.com/p/gerrit/)
 #
@@ -27,7 +26,7 @@ MSG="$1"
 #
 add_ChangeId() {
 	clean_message=`sed -e '
-		/^diff --git a\/.*/{
+		/^diff --git .*/{
 			s///
 			q
 		}
@@ -39,6 +38,11 @@ add_ChangeId() {
 		return
 	fi
 
+	if test "false" = "`git config --bool --get gerrit.createChangeId`"
+	then
+		return
+	fi
+
 	# Does Change-Id: already exist? if so, exit (no change).
 	if grep -i '^Change-Id:' "$MSG" >/dev/null
 	then
@@ -77,7 +81,7 @@ add_ChangeId() {
 	# Skip the line starting with the diff command and everything after it,
 	# up to the end of the file, assuming it is only patch data.
 	# If more than one line before the diff was empty, strip all but one.
-	/^diff --git a/ {
+	/^diff --git / {
 		blankLines = 0
 		while (getline) { }
 		next