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--pre-commit.sample

@@ -0,0 +1,70 @@
+#!/bin/sh
+#
+# An example hook script to verify what is about to be committed.
+# Called by git-commit with no arguments.  The hook should
+# exit with non-zero status after issuing an appropriate message if
+# it wants to stop the commit.
+#
+# To enable this hook, rename this file to "pre-commit".
+
+# This is slightly modified from Andrew Morton's Perfect Patch.
+# Lines you introduce should not have trailing whitespace.
+# Also check for an indentation that has SP before a TAB.
+
+if git-rev-parse --verify HEAD 2>/dev/null
+then
+	git-diff-index -p -M --cached HEAD --
+else
+	# NEEDSWORK: we should produce a diff with an empty tree here
+	# if we want to do the same verification for the initial import.
+	:
+fi |
+perl -e '
+    my $found_bad = 0;
+    my $filename;
+    my $reported_filename = "";
+    my $lineno;
+    sub bad_line {
+	my ($why, $line) = @_;
+	if (!$found_bad) {
+	    print STDERR "*\n";
+	    print STDERR "* You have some suspicious patch lines:\n";
+	    print STDERR "*\n";
+	    $found_bad = 1;
+	}
+	if ($reported_filename ne $filename) {
+	    print STDERR "* In $filename\n";
+	    $reported_filename = $filename;
+	}
+	print STDERR "* $why (line $lineno)\n";
+	print STDERR "$filename:$lineno:$line\n";
+    }
+    while (<>) {
+	if (m|^diff --git a/(.*) b/\1$|) {
+	    $filename = $1;
+	    next;
+	}
+	if (/^@@ -\S+ \+(\d+)/) {
+	    $lineno = $1 - 1;
+	    next;
+	}
+	if (/^ /) {
+	    $lineno++;
+	    next;
+	}
+	if (s/^\+//) {
+	    $lineno++;
+	    chomp;
+	    if (/\s$/) {
+		bad_line("trailing whitespace", $_);
+	    }
+	    if (/^\s* \t/) {
+		bad_line("indent SP followed by a TAB", $_);
+	    }
+	    if (/^([<>])\1{6} |^={7}$/) {
+		bad_line("unresolved merge conflict", $_);
+	    }
+	}
+    }
+    exit($found_bad);
+'