[PATCH 0 of 4] Add Schemas

[Durham Goode]

This series is part RFC and part actual patch.  In particular:

- Can anyone think of a better name than 'schema'?

- How do people feel about the security implications?  If a user pulls from an untrusted source they could have a malicious schema introduced.  For example, if they have largefiles enabled and pull from a malicious user, their schema could be changed such that they request largefiles from a malicious location.  On the other hand, this doesn't seem any different from the security concerns of pulling from an untrusted location the old fashioned way.