Ship sample hooks with .sample suffix

We used to mark hooks we ship as samples by making them unexecutable, but
some filesystems cannot tell what is executable and what is not.

This makes it much more explicit.  The hooks are suffixed with .sample
(but now are made executable), so enabling it is still one step operation
(instead of "chmod +x $hook", you would do "mv $hook.sample $hook") but
now they won't get accidentally enabled on systems without executable bit.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

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

@@ -0,0 +1,36 @@
+#!/bin/sh
+#
+# An example hook script to prepare the commit log message.
+# Called by git-commit with the name of the file that has the
+# commit message, followed by the description of the commit
+# message's source.  The hook's purpose is to edit the commit
+# message file.  If the hook fails with a non-zero status,
+# the commit is aborted.
+#
+# To enable this hook, rename this file to "prepare-commit-msg".
+
+# This hook includes three examples.  The first comments out the
+# "Conflicts:" part of a merge commit.
+#
+# The second includes the output of "git diff --name-status -r"
+# into the message, just before the "git status" output.  It is
+# commented because it doesn't cope with --amend or with squashed
+# commits.
+#
+# The third example adds a Signed-off-by line to the message, that can
+# still be edited.  This is rarely a good idea.
+
+case "$2,$3" in
+  merge,)
+    perl -i -ne 's/^/# /, s/^# #/#/ if /^Conflicts/ .. /#/; print' "$1" ;;
+
+# ,|template,)
+#   perl -i -pe '
+#      print "\n" . `git diff --cached --name-status -r`
+#	 if /^#/ && $first++ == 0' "$1" ;;
+
+  *) ;;
+esac
+
+# SOB=$(git var GIT_AUTHOR_IDENT | sed -n 's/^\(.*>\).*$/Signed-off-by: \1/p')
+# grep -qs "^$SOB" "$1" || echo "$SOB" >> "$1"