Fix for Lua script when removing a huge amount of keys in _removeByMatchingAnyTags()

Hi Collin,

I'm using Cm_Cache_Backend_Redis on a very large Magento shop which easily generates up to 1.000.000 keys within a few hours.

Recently, when refreshing for example the Block Html cache, we've experienced an error:
```
too many results to unpack
```

So I have added a small change to the Lua script in the ```_removeByMatchingAnyTags()``` method to process the Redis calls in 10000 keys steps.

Please take a look and see if it makes sense. Maybe you have a better approach?

Thanks!