cvsimport: apply shell-quoting regex globally

Commit 5b4efea (cvsimport: shell-quote variable used in
backticks, 2017-09-11) tried to shell-quote a variable, but
forgot to use the "/g" modifier to apply the quoting to the
whole variable. This means we'd miss any embedded
single-quotes after the first one.

Reported-by: <[email protected]>
Signed-off-by: Jeff King <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: peff

git-cvsimport.perl

@@ -642,7 +642,7 @@ sub is_sha1 {
 
 sub get_headref ($) {
 	my $name = shift;
-	$name =~ s/'/'\\''/;
+	$name =~ s/'/'\\''/g;
 	my $r = `git rev-parse --verify '$name' 2>/dev/null`;
 	return undef unless $? == 0;
 	chomp $r;