clean up TargetFramework

use TargetFramework as before for "2.0.50727", "4.0", etc. Use
TargetFrameworkVersion for the original value of "v2.0", "v4.0", etc.


git-svn-id: https://svn.apache.org/repos/asf/incubator/npanday/trunk@1451807 13f79535-47bb-0310-9956-ffa450edef68