Update to 6.x needs batch mode

Here is a first crack at implementing a batch upgrade path to go from D5 to D6. I have not yet tested it on a large site but it seems to work on a small, local test website. I'll have a fresh look at it in a couple of hours -- in the mean time, feel free to do a quick review or do do some testing.

Looks good except for the potential notice on $_SESSION['comment_upload_update_6000']++. Is there a reason for the count, or could we simply use this as a flag?

Run on a drupal.org database dump on a beefy server seems to be not affected by any timeout. However, it does not guarantee that the run on drupal.org will not get timed out.

The updated code uses two "select into" queries for speed rather than looping if db = mysql. Setting back to active so I remember to patch for non-mysql databases.

Since drupal.org uses MySQL and this has good performance on MySQL, it works for us.

I found http://cvs.drupal.org/viewvc.py/drupal/contributions/modules/comment_upl..., apparently slipped in with another commit (?).

Needs a rollback, as this FUBARed the files table of do.

David Strauss:

Doesn't work when $db_url is an array. ($db_type should be used).

autoincrement is not consistent between table engines; the INSERT INTO .. SELECT has to go.

This should get cleaned up and resolved before a 6.x-1.0 release.