dirstate-v2: Reuse existing nodes when appending to a data file...
dirstate-v2: Reuse existing nodes when appending to a data file
When writing a dirstate in v2 format by appending to an existing data file,
nodes that are still "unparsed" from the previous on-disk representation
have been unchanged and can therefore be reused.
This makes the new data point to previously-existing data for tree nodes.
Differential Revision:
https://phab.mercurial-scm.org/D11095
