[Java] Check for keyword as a formatted field name. Issue aeron-io#317

Author: mjpt777

sbe-tool/src/main/java/uk/co/real_logic/sbe/xml/Field.java

@@ -91,7 +91,7 @@ public void validate(final Node node)
  }
  }
 
- checkForValidName(node, name);
+ checkForValidName(node, Character.toLowerCase(name.charAt(0)) + name.substring(1));
 
  if (type instanceof EnumType && presence == Presence.CONSTANT)
  {