TODO: limit to large syncs?
This needs a lot of testing.
Also:
- Tweak pumpGenerator() wait level behavior to match Zotero.wait()
- If Zotero is closed in the top-most window, show a popup instead of the pane-covering progress meter, and take an optional icon in Zotero.showZoteroPaneProgressMeter() for use in the popup
- Restore protection against opening Zotero pane when Zotero.locked is set
- Display a nicer error if Zotero.DB.commitTransaction() is called without an active transaction
- Allow text with icons to extend to multiple lines in progressWindow popup
- Automatically use current window if one isn't specified in Zotero.repaint()
