New ~/Library/Keychains subfolder?

I've been using OS X 10.7 Lion until today, and I've just bought an SSD for my Macbook (to upgrade from a harddrive) and installed OS X 10.9 Mavericks on it.

So far Mavericks seems great, and there are some sweet little improvements. I've put my old hard-drive in an external USB enclosure, and I'm copying my preferences files over.

During the course of this, it seems like the organistion structure of ~/Library/Keychains has changed.

On my old 10.7 system I had the files Microsoft_Intermediate_Certificates, login.keychain, metadata.keychain

On my new 10.9 system I have only the file login.keychain and then a separate subfolder called 833385D1-2681-5706-B6E9-8C1BDCA4928E

In the subfolder are: accountStatus.plist, keychain-2.db, keychain-2.db-shm. keychain-2.db-wal, user.kb

I assume that I can copy over my old login.keychain and all my passwords will transfer, but what is the subfolder with the funny name for?

I can't think of anything I've used (in the last couple of hours of setting up preferences on this new computer) which could have created it. I'm almost tempted to delete the **** thing, and see what breaks. 😉