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/xact.h b/src/xact.h
index 4882acd2..4c6fcd73 100644
--- a/src/xact.h
+++ b/src/xact.h
@@ -127,6 +127,8 @@ public:
                                   const string& name);
 
   virtual bool valid() const;
+
+  virtual string hash(string nonce) const;
 };
 
 class auto_xact_t : public xact_base_t