Improvements to protocol serialization:

A few serialization changes coming from m-of-n development:

 o Improve readability of SField.cpp.
 o Better initialization of STObject.
 o Trimming of STObject public methods.
 o Add STObject::getFieldObject and STObject::setFieldObject.
 o Make STObject::isEquivalent more robust.
 o Improvements to whitespace, overrides, and virtuals.

src/ripple/protocol/impl/STTx.cpp

@@ -155,7 +155,7 @@ static Blob getSigningData (STTx const& that)
 {
     Serializer s;
     s.add32 (HashPrefix::txSign);
-    that.add (s, false);
+    that.addWithoutSigningFields (s);
     return s.getData();
 }