Several small cleanups & speed-ups

- Call _request directly from convenience wrappers in restbase
- Add fast path in makeRequest
- Replace a bind with a closure in storage.js (for a minor perf gain), and fix
  a warn to actually use the 'warn' level instead of 'warning'
- Add level filtering right in the log method, and streamline the
  simplification process at the same time.
- Default to logging at the 'warn' level.