BP 2.5: Set the 'Reply-To' email header in a different way.

The BP_PHPMailer class uses PHPMailer's addReplyTo() method to set the
'Reply-To' email header.  This method has a bug where it will not add
email addresses with a mailbox larger than 64 characters. See:
github.com/PHPMailer/PHPMailer/issues/706 for more details.

In cases where RBE's Reply-To email address mailbox might surpass 64
characters, BP_PHPMailer would silently discard our Reply-To email
address!

To workaround this bug, we're wiping out the Reply-To header and re-adding
it with custom email headers, which bypasses PHPMailer's validation
address checks.

See #75.

bp-rbe-core.php

@@ -240,8 +240,18 @@ public function set_bp_reply_to( $email_type, $email ) {
 			return;
 		}
 
-		// Set our custom 'Reply-To' email header.
-		$email->set_reply_to( $reply_to );
+		/**
+		 * Set our custom 'Reply-To' email header.
+		 *
+		 * Have to workaround a mailbox character limit PHPMailer bug by wiping out
+		 * the Reply-To header and then setting it as a custom header.
+		 *
+		 * @link https://github.com/PHPMailer/PHPMailer/issues/706
+		 */
+		$email->set_reply_to( '' );
+		$email->set_headers( array(
+			'Reply-To' => $reply_to
+		) );
 	}
 
 	/**