t/annotate-tests: Use echo & cat instead of sed

The use of the sed command "1i No robots allowed" caused the version
of sed in OS X to die with

   sed: 1: "1i "No robots allowed"\n": command i expects \ followed by
   text

Since this command was just trying to add a single line to the
beginning of the file, do the same with "echo" followed by "cat".

Unbreaks t8001 and t8002 on OS X 10.6.7
Signed-off-by: NBrian Gernhardt <brian@gernhardtsoftware.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

t/annotate-tests.sh

@@ -127,7 +127,8 @@ test_expect_success \
 
 test_expect_success \
     'an obfuscated email added' \
-    'sed -e "1i No robots allowed" < file > file.new &&
+    'echo "No robots allowed" > file.new &&
+     cat file >> file.new &&
      mv file.new file &&
      GIT_AUTHOR_NAME="E" GIT_AUTHOR_EMAIL="E at test dot git" git commit -a -m "norobots"'