Don't try to save which options were used to load the data

[shashi]

loadfiles hashes the options passed to it to make sure we don't use invalid cached data. We should instead just warn about this when we are using cache, and allow user to say overwritecache=true to invalidate it. Always load data from cache.

[JeffBezanson]

It works better now, but we are still saving the options that were passed. It's mostly harmless, but unnecessary and increases the size of the index. It also adds risk of something going wrong, in case there's something strange in the options we can't deserialize (e.g. a function in a package that's not loaded anymore).

[shashi]

We don't save the hash of the options in the metadata anymore. We only use it to key _read_cache dictionary - which is more harmless since objects are only needed to have the same hash in a given session and not across sessions.

[JeffBezanson]

We are still saving the options themselves, as part of the chunk objects.

[shashi]

Well usecache=false should make that get overwritten as well. I'm now a bit unclear what we should be doing instead.

[shashi]

We removed usecache.