Fix processing of double metadata replacements

Transactions that replaced metadata twice at the same offset
(with retainMeta-replaceMeta-retainMeta-replaceMeta) were broken
because the processor for replaceMetadata didn't advance the
metadata cursor.

Change-Id: I7ad24e7ffb4c39b40ec9c347db301f8e28f3692d
Allow replace operations to replace metadata as well

This was already possible in the operation structure by using
removeMetadata and insertMetadata, but no transaction builders
generated transactions like that.

With this change, pushReplace() can be instructed to overwrite the
metadata with arbitrary data rather than collapsing it by passing the
optional insertMeta parameter.

Change-Id: I0272fe38e053161c738591cf0a7b447a0827d4dc
Rewrite MetaList.onTransact

The previous implementation couldn't deal with transactions that
replaced both data and metadata at the same time (rather than replacing
data while moving metadata around), and extending its approach to
deal with that case would have made it much more complex.

So I rewrote the algorithm from scratch. The previous implementation
scheduled deferred moves for existing items, but immediately processed
insertions and removals. This is problematic for replacements and
maintaining the order in the binary search list. So instead, this new
implementation builds an array representing what the new item list
should be, then processes insertions, removals and moves in the correct
order to achieve that state.

It looks like the previous implementation didn't always work correctly,
which was masked because the test suite passed full=false to
assertItemsMatchMetadata(). This rewrite fixes this.

Also remove setMove/applyMove from MetaItem, because we don't need them
anymore and they're evil anyway; and add isAttached(), because the new
algorithm needs it.

Change-Id: I899d2b3c94c2cfa55823879bca95456750f64382
Merge changes I899d2b3c,I0272fe38,I7ad24e7f

* changes:
  Rewrite MetaList.onTransact
  Allow replace operations to replace metadata as well
  Fix processing of double metadata replacements