Add support for hash chaining to detect modifications in postings

The following details of a posting contribute to its hash:

  fullname of account
  string representation of amount

Each posting hashes contributes to the transaction hash, which is compromised
of:

  previous transaction’s hash (as encountered in parsing order)
  actual date
  optional auxiliary date
  optional code
  payee
  hashes of all postings

Note that this means that changes in the “code” or any of the comments

1 files changed, 2 insertions, 0 deletions

diff --git a/src/post.h b/src/post.h
index 48b614bf..48093463 100644
--- a/src/post.h
+++ b/src/post.h
@@ -245,6 +245,8 @@ public:
     return const_cast<post_t *>(this)->reported_account();
   }
 
+  virtual string hash(string nonce) const;
+
   friend class xact_t;
 
   struct compare_by_date_and_sequence