Fix use of "perl -i" on Windows

The perldiag(1) has following to say about this:

    "Can't do inplace edit without backup"

	(F) You're on a system such as MS-DOS that gets confused if
	you try reading from a deleted (but still opened) file. You
	have to say -i.bak, or some such.

Signed-off-by: Alex Riesen <raa.lkml@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

templates/hooks--prepare-commit-msg.sample

@@ -22,10 +22,10 @@
 
 case "$2,$3" in
   merge,)
-    perl -i -ne 's/^/# /, s/^# #/#/ if /^Conflicts/ .. /#/; print' "$1" ;;
+    perl -i.bak -ne 's/^/# /, s/^# #/#/ if /^Conflicts/ .. /#/; print' "$1" ;;
 
 # ,|template,)
-#   perl -i -pe '
+#   perl -i.bak -pe '
 #      print "\n" . `git diff --cached --name-status -r`
 #	 if /^#/ && $first++ == 0' "$1" ;;