Porcelain scripts: Rewrite cryptic "needs update" error message

Although Git interally has the facility to differentiate between
porcelain and plubmbing commands and appropriately print errors,
several shell scripts invoke plubming commands triggering cryptic
plumbing errors to be displayed on a porcelain interface. This patch
replaces the "needs update" message in git-pull and git-rebase, when
`git update-index` is run, with a more friendly message.

Reported-by: Joshua Jensen <jjensen@workspacewhiz.com>
Reported-by: Thore Husfeldt <thore.husfeldt@gmail.com>
Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-pull.sh

@@ -201,10 +201,7 @@ test true = "$rebase" && {
 			die "updating an unborn branch with changes added to the index"
 		fi
 	else
-		git update-index --ignore-submodules --refresh &&
-		git diff-files --ignore-submodules --quiet &&
-		git diff-index --ignore-submodules --cached --quiet HEAD -- ||
-		die "refusing to pull with rebase: your working tree is not up-to-date"
+		require_clean_work_tree "pull with rebase" "Please commit or stash them."
 	fi
 	oldremoteref= &&
 	. git-parse-remote &&

git-rebase--interactive.sh

@@ -153,14 +153,6 @@ run_pre_rebase_hook () {
 	fi
 }
 
-require_clean_work_tree () {
-	# test if working tree is dirty
-	git rev-parse --verify HEAD > /dev/null &&
-	git update-index --ignore-submodules --refresh &&
-	git diff-files --quiet --ignore-submodules &&
-	git diff-index --cached --quiet HEAD --ignore-submodules -- ||
-	die "Working tree is dirty"
-}
 
 ORIG_REFLOG_ACTION="$GIT_REFLOG_ACTION"
 
@@ -557,7 +549,7 @@ do_next () {
 			exit "$status"
 		fi
 		# Run in subshell because require_clean_work_tree can die.
-		if ! (require_clean_work_tree)
+		if ! (require_clean_work_tree "rebase")
 		then
 			warn "Commit or stash your changes, and then run"
 			warn
@@ -768,7 +760,7 @@ first and then run 'git rebase --continue' again."
 
 		record_in_rewritten "$(cat "$DOTEST"/stopped-sha)"
 
-		require_clean_work_tree
+		require_clean_work_tree "rebase"
 		do_rest
 		;;
 	--abort)
@@ -866,7 +858,7 @@ first and then run 'git rebase --continue' again."
 
 		comment_for_reflog start
 
-		require_clean_work_tree
+		require_clean_work_tree "rebase" "Please commit or stash them."
 
 		if test ! -z "$1"
 		then

git-rebase.sh

@@ -416,19 +416,7 @@ else
 	fi
 fi
 
-# The tree must be really really clean.
-if ! git update-index --ignore-submodules --refresh > /dev/null; then
-	echo >&2 "cannot rebase: you have unstaged changes"
-	git diff-files --name-status -r --ignore-submodules -- >&2
-	exit 1
-fi
-diff=$(git diff-index --cached --name-status -r --ignore-submodules HEAD --)
-case "$diff" in
-?*)	echo >&2 "cannot rebase: your index contains uncommitted changes"
-	echo >&2 "$diff"
-	exit 1
-	;;
-esac
+require_clean_work_tree "rebase" "Please commit or stash them."
 
 if test -z "$rebase_root"
 then

git-sh-setup.sh

@@ -145,6 +145,35 @@ require_work_tree () {
 	die "fatal: $0 cannot be used without a working tree."
 }
 
+require_clean_work_tree () {
+	git rev-parse --verify HEAD >/dev/null || exit 1
+	git update-index -q --ignore-submodules --refresh
+	err=0
+
+	if ! git diff-files --quiet --ignore-submodules
+	then
+		echo >&2 "Cannot $1: You have unstaged changes."
+		err=1
+	fi
+
+	if ! git diff-index --cached --quiet --ignore-submodules HEAD --
+	then
+		if [ $err = 0 ]
+		then
+		    echo >&2 "Cannot $1: Your index contains uncommitted changes."
+		else
+		    echo >&2 "Additionally, your index contains uncommitted changes."
+		fi
+		err=1
+	fi
+
+	if [ $err = 1 ]
+	then
+		test -n "$2" && echo >&2 "$2"
+		exit 1
+	fi
+}
+
 get_author_ident_from_commit () {
 	pick_author_script='
 	/^author /{