Introduce FullTx type exposed by ChainBuilder

This contains _all_ information that happened in a transaction (for
instance, including the exact contracts that were deployed). The
ChainBuilder exposes the trace of transactions (as FullTx values) that
have happened in the chain.

src/Blockchain.v

@@ -306,6 +306,10 @@ Record ChainBuilderInterface :=
                     Address (* coinbase *) ->
                     list (Address * ChainAction) (* actions *) ->
                     option cbi_type;
+    (* List of transactions that have been executed on the chain, in order.
+That is, the head of the list corresponds to actions in the very first block.
+This includes "internal" transactions (txs resulting from contract execution) *)
+    cbi_all_txs : cbi_type -> list FullTx;
   }.
 
 Record ChainBuilder :=
@@ -331,3 +335,7 @@ Definition add_block
   let (ifc, val) := cur in
   let new_val := ifc.(cbi_add_block) val coinbase actions in
   option_map (build_chain_builder ifc) new_val.
+
+Definition all_txs (cb : ChainBuilder) :=
+  let (ifc, val) := cb in
+  ifc.(cbi_all_txs) val.

src/Extras.v

@@ -10,3 +10,13 @@ Fixpoint find_first {A B : Type} (f : A -> option B) (l : list A)
                 end
   | [] => None
   end.
+
+Fixpoint map_option {A B : Type} (f : A -> option B) (l : list A)
+  : list B :=
+  match l with
+  | hd :: tl => match f hd with
+                  | Some b => b :: map_option f tl
+                  | None => map_option f tl
+                end
+  | [] => []
+  end.