XMLList should not include "space" Node.

[Tao Liang]

The function "void XMLList::buildFromString(const std::string& str)" will build "space" node into XMLList. I think this is not the right behavior.
The following is the code snippet:

xmlpp::Node::NodeList::const_iterator it;
 for(it=children.begin(); it!=children.end(); ++it)
  nodes.push_back(_MR(Class<XML>::getInstanceS(*it)));

From the above code, xml ContentNode which represents space or comment will be push back into nodes.
I think ContentNode should be skipped.