Allow '(no author)' in git-svn's authors file.

When trying to import an SVN revision which has no author the Git
user may desire to relabel '(no author)' to another name and email
address with their svn.authorsfile.
Signed-off-by: NShawn O. Pearce <spearce@spearce.org>
Signed-off-by: NJunio C Hamano <junkio@cox.net>

git-svn.perl

@@ -2171,7 +2171,7 @@ sub load_authors {
 	open my $authors, '<', $_authors or die "Can't open $_authors $!\n";
 	while (<$authors>) {
 		chomp;
-		next unless /^(\S+?)\s*=\s*(.+?)\s*<(.+)>\s*$/;
+		next unless /^(\S+?|\(no author\))\s*=\s*(.+?)\s*<(.+)>\s*$/;
 		my ($user, $name, $email) = ($1, $2, $3);
 		$users{$user} = [$name, $email];
 	}