* Add $wgLegacySchemaConversion update-time option to reduce amount of

* Add $wgLegacySchemaConversion update-time option to reduce amount of
  copying during the schema upgrade: creates HistoryBlobCurStub reference
  records in text instead of copying all the cur_text fields. Requires
  that the cur table be left in place until/unless such fields are migrated
  into the main text store.

In my test with a nl.wikipedia.org dump, this sped up the cur-to-old copy
operation from a few hours to a few minutes. Also added some hacky timer
echos in the updater for debug purposes. They should be prettied up but
probably kept.