SendEmail Reactor accept Content-type from template

[Doug Kyle]

I wanted to send html from AT event templates, so made SendEmail reactor accept the Content-type header.

--- a/2_11/lib/OpenILS/Application/Trigger/Reactor/SendEmail.pm
+++ b/2_11/lib/OpenILS/Application/Trigger/Reactor/SendEmail.pm
@@ -58,13 +58,13 @@ sub handler {

     my $email = Email::Simple->new($text);

- for my $hfield (qw/From To Subject Bcc Cc Reply-To Sender/) {
+ for my $hfield (qw/From To Subject Bcc Cc Reply-To Sender Content-Type/) {
  my @headers = $email->header($hfield);
  $email->header_set($hfield => map { encode("MIME-Header", $_) } @headers) if ($headers[0]);
     }

     $email->header_set('MIME-Version' => '1.0');
- $email->header_set('Content-Type' => "text/plain; charset=UTF-8");
+ $email->header_set('Content-Type' => "text/plain; charset=UTF-8") unless $email->header('Content-Type');
     $email->header_set('Content-Transfer-Encoding' => '8bit');

     try {