Reduce memory requirements

Right now the parser has very large memory requirements. I had to up my local install's available memory to run the parsing for core. 2GB on the VM and 1GB for PHP. This has some headroom, but it's regularly taking around 400MB to parse core initially and 320MB on an subsequent update run. The import script can run hundreds of thousands of queries, a simply put, PHP isn't meant to run for long periods of time so it leaks.

I would love to see some work done to audit where the memory leaks are and shore the worst ones up. I did a little bit of exploring and was able to determine that parsing should never be done with the SAVEQUERIES constant set to true. That should have been obvious, but I have it on for all my dev sites and I didn't think about it saving queries eating up memory during the cli call. Turning this off alone halves the memory requirement (~800MB before turning it off).

Nothing else I have explored has helped much, and some of it even increased the requirements. It'll take some digging because memory tools in PHP are rudimentary at best.

Start with the parser's import run for core and compare memory usage with the PHP SAVEQUERIES constant disabled, since the issue identifies this as a major contributor. Then investigate the remaining memory growth during the initial parse and subsequent update runs. Done means materially reducing the reported peak memory requirements without changing parsing results.