t3702: abstract away SHA-1-specific constants

Strip out the index lines in the diff before comparing them, as these
will differ between hash algorithms.  This leads to a smaller, simpler
change than editing the index line.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t3702-add-edit.sh

@@ -40,7 +40,6 @@ test_expect_success 'setup' '
 
 cat > expected-patch << EOF
 diff --git a/file b/file
-index b9834b5..9020acb 100644
 --- a/file
 +++ b/file
 @@ -1,11 +1,6 @@
@@ -80,7 +79,6 @@ EOF
 
 cat > expected << EOF
 diff --git a/file b/file
-index b9834b5..ef6e94c 100644
 --- a/file
 +++ b/file
 @@ -1,10 +1,12 @@
@@ -100,7 +98,7 @@ EOF
 
 echo "#!$SHELL_PATH" >fake-editor.sh
 cat >> fake-editor.sh <<\EOF
-mv -f "$1" orig-patch &&
+egrep -v '^index' "$1" >orig-patch &&
 mv -f patch "$1"
 EOF
 
@@ -113,7 +111,8 @@ test_expect_success 'add -e' '
 	git add -e &&
 	test_cmp second-part file &&
 	test_cmp orig-patch expected-patch &&
-	git diff --cached > out &&
+	git diff --cached >actual &&
+	grep -v index actual >out &&
 	test_cmp out expected
 
 '