Rekey the template_attachments table. Fixes bug #11063.

Also, prevent template attachments from throwing an error on duplicate
URLs, and fix the purge method added earlier.

docs/changelog/7.x.x.txt

@@ -3,6 +3,7 @@
  - fixed #11152: Image edits do not autocommit version tags
  - fixed template attachments are not cleaned up during purge
  - fixed #11150: matrix - search boxes all ticked
+ - fixed #11063: template_attachments
 
 7.8.2
  - Added scheduled vendor payout workflow activity. (Special thanks to Martin @ Oqapi)

docs/upgrades/upgrade_7.8.2-7.8.3.pl

@@ -31,12 +31,30 @@ my $quiet; # this line required
 my $session = start(); # this line required
 
 # upgrade functions go here
+reKeyTemplateAttachments($session);
 
 finish($session); # this line required
 
 
 #----------------------------------------------------------------------------
 # Describe what our function does
+sub reKeyTemplateAttachments {
+    my $session = shift;
+    print "\tChanging the key structure for the template attachments table... " unless $quiet;
+    # and here's our code
+    $session->db->write('ALTER TABLE template_attachments ADD COLUMN attachId CHAR(22) BINARY NOT NULL');
+    my $rh = $session->db->read('select url, templateId, revisionDate from template_attachments');
+    my $wh = $session->db->prepare('update template_attachments set attachId=? where url=? and templateId=? and revisionDate=?');
+    while (my @key = $rh->array) {
+        $wh->execute([$session->id->generate, @key ]);
+    }
+    $rh->finish;
+    $wh->finish;
+    $session->db->write('ALTER TABLE template_attachments DROP PRIMARY KEY');
+    $session->db->write('ALTER TABLE template_attachments ADD PRIMARY KEY (attachId)');
+    print "DONE!\n" unless $quiet;
+}
+
 #sub exampleFunction {
 #    my $session = shift;
 #    print "\tWe're doing some stuff here that you should know about... " unless $quiet;