lazymanifest: use a binary search to do an insertion This makes insertions log(n) plus some memmove() overhead, rather than doing an append followed by an n*log(n) sort. There's probably a lot of performance to be gained by adding a batch-add method, which could be smarter about the memmove()s performed. Includes a couple of extra tests that should help prevent bugs. Thanks to Martin for some significant pre-mail cleanup of this change.