[Java] Improve validation of valueRef on fields.

Author: mjpt777

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

@@ -110,14 +110,14 @@ public void validate(final Node node)
  final String valueRefType = valueRef.substring(0, periodIndex);
  if (!valueRefType.equals(type.name()))
  {
- handleError(node, "valueRef Enum type not found: " + valueRefType);
+ handleError(node, "valueRef for Enum name not found: " + valueRefType);
  }
 
  final String validValueName = valueRef.substring(periodIndex + 1);
  final EnumType enumType = (EnumType)type;
  if (null == enumType.getValidValue(validValueName))
  {
- handleError(node, "valueRef Valid value name not found: " + validValueName);
+ handleError(node, "valueRef for validValue name not found: " + validValueName);
  }
  }
  }