code: protected void makeConstructorDoc(MethodSymbol meth, TreePath treePath) {
          ConstructorDocImpl result = (ConstructorDocImpl)methodMap.get(meth);
          if (result != null) {
              if (treePath != null) result.setTreePath(treePath);
          } else {
              result = new ConstructorDocImpl(this, meth, treePath);
              methodMap.put(meth, result);
          }
      }
docs: Create the ConstructorDoc for a MethodSymbol.
  Should be called only on symbols representing constructors.