Implement new amendment majority semantics :

This implements the tracking of when an amendment achieved a majority
in the ledger, ensuring that there's always network-wide agreement
on which amendments have achieved a majority and how long they've
held it.

* New fields
* Change transactor changes
* AmendmentTable API and implementation changes
* Update amendment enabled status on validated ledgers
* Reinstate support for ledger sequence in fee transactions

src/ripple/ledger/impl/View.cpp

@@ -23,6 +23,7 @@
 #include <ripple/basics/Log.h>
 #include <ripple/basics/StringUtilities.h>
 #include <ripple/protocol/Quality.h>
+#include <ripple/protocol/STArray.h>
 
 namespace ripple {
 
@@ -388,6 +389,37 @@ cdirNext (ReadView const& view,
     return true;
 }
 
+enabledAmendments_t
+getEnabledAmendments (ReadView const& view)
+{
+    enabledAmendments_t amendments;
+    auto const sleAmendments = view.read(keylet::amendments());
+
+    if (sleAmendments)
+    {
+        for (auto const &a : sleAmendments->getFieldV256 (sfAmendments))
+            amendments.insert (a);
+    }
+
+    return amendments;
+}
+
+majorityAmendments_t
+getMajorityAmendments (ReadView const& view)
+{
+    majorityAmendments_t majorities;
+    auto const sleAmendments = view.read(keylet::amendments());
+
+    if (sleAmendments && sleAmendments->isFieldPresent (sfMajorities))
+    {
+        auto const& majArray = sleAmendments->getFieldArray (sfMajorities);
+        for (auto const& m : majArray)
+            majorities[m.getFieldH256 (sfAmendment)] = m.getFieldU32 (sfCloseTime);
+    }
+
+    return majorities;
+}
+
 //------------------------------------------------------------------------------
 //
 // Modifiers