annotate: fix -S parameter to take a string

In the conversion to Getopt::Long, the -S / --rev-list parameter stopped
working. We need to tell Getopt::Long that it is a string.

As a bonus, the open() now does some useful error handling.
Signed-off-by: NMartin Langhoff <martin@catalyst.net.nz>
Signed-off-by: NJunio C Hamano <junkio@cox.net>

git-annotate.perl

@@ -31,7 +31,7 @@ ()
 my $rc = GetOptions(	"long|l" => \$longrev,
 			"help|h" => \$help,
 			"rename|r" => \$rename,
-			"rev-file|S" => \$rev_file);
+			"rev-file|S=s" => \$rev_file);
 if (!$rc or $help) {
 	usage();
 }
@@ -174,7 +174,8 @@ sub git_rev_list {
 
 	my $revlist;
 	if ($rev_file) {
-		open($revlist, '<' . $rev_file);
+		open($revlist, '<' . $rev_file)
+		    or die "Failed to open $rev_file : $!";
 	} else {
 		$revlist = open_pipe("git-rev-list","--parents","--remove-empty",$rev,"--",$file)
 			or die "Failed to exec git-rev-list: $!";