Stripping lib prefix from Mingw builds.

[JTippetts]

A recent commit has started stripping the lib prefix from static library builds. Is this the desired behavior? I build a custom executable external to the Urho3D build framework (a project in Code::Blocks) and it needs to have the prefix in order to find the library, forcing me to rename it after a new build. I hate the idea of the manual renaming, since I just know I'm going to forget it one of these days and end up linking against an older version.