Split SQL batches correctly around dollar quotes and comments

splitStatements() only knew 'strings' and "identifiers", so a DO block
or function body ($$ ... ; ... $$) was cut at its inner semicolons and
failed, and a quote inside a comment (-- don't) opened a string that
never closed. It now also skips dollar-quoted bodies, E'...' strings
with backslash escapes, and comments. It moves to SqlGuard so it is
tested with the other checks.

OccController::run() now catches Throwable, so an Error thrown by a
command is logged and returned like an Exception instead of ending in
an HTTP 500.

Not changed on purpose: showing rows for statements with RETURNING or
data-modifying CTEs, and failure handling in the Makefile release
targets. Both came up in the same review but are unrelated to the
security fixes in this release.

lib/Controller/OccController.php

@@ -91,7 +91,7 @@ class OccController extends Controller
     try {
       $this->application->run($input, $this->output);
       return $this->output->fetch();
-    } catch (Exception $ex) {
+    } catch (\Throwable $ex) {
       $this->logger->error($ex->getMessage(), ['exception' => $ex]);
       return "error: " . $ex->getMessage();
     }