rev 6327cda0a tried to workaround the fact that the assets bundle were
unreadable when they are created in the same request by opening multiple
cursors and commiting the writes in ir.attachment. Sadly, this strategy
introduces sometimes hard to reproduce and hard to understand deadlocks
when regenerating the assets. This commit tries a ~safer strategy by not
opening multiple cursors but commiting the writes in ir.attachment when
a magic key is in the context.
Simon Lejeune
58ae39945a