Use massupdate for updating indexes, much faster

[paales]

In AvS_FastSimpleImport we use the following code to update indexes as fast as possible:
https://github.com/avstudnitz/AvS_FastSimpleImport/blob/master/src/app/code/community/AvS/FastSimpleImport/Model/Import/Entity/Product.php#L476-L532

As far as I can tell, this module runs the update per event and not as a whole, so there is room for improvement.

[Flyingmana]

would need some tests, we try to have the indexer as non blocking as possible and a massupdate could be problematic.

Also you hit some conditions where you instead trigger an reindexAll which is absolutely blocking and not ok for this async indexer.
And it depends strongly on the kind of index, some of them still seem to loop, while others do a bit of magic.