Should make Folder_reindexAll and most custom indexation methods obsolete.
Remaining valid reindexation methods are:
- reindexObject: for a single document, which may contain subdocuments
  which indexation is not necessary
- recursiveReindexobject: for any subtree of documents
- ERP5Site_reindexAll: for site-wide reindexations, as there is a semantic-
  dependent indexation order.

Also, uniformise and factorise spawning immediateReindexObject.

Also:
- testSupply: Drop check for the previous magic threshold.
  _recurseCallMethod takes care of it all now.
- testXMLMatrix: Let activities execute before changing cell id.
  This works only because recursiveReindexObject on the matrix spawns a
  single recursiveImmediateReindexObject activity on that context. Now,
  up to 1k immediateReindexObject activities (for the first 1k sub-objects)
  are spawned immediately, preventing their renaming immediately after
  commit.
  So let test wait for indexation before trying to rename.
- testERP5Security: More activities are now spawned immediately, adapt.