Hack particular gccxml location for one particular nightly build machine.

Incorporate Normal Mode Langevin openmm code from Chris Sweet as a plugin.  (compiles on windows, but no actual testing done)

plugins/normalModeLangevin/test/TestNormalModeLangevin.cpp

+#include "OpenMM.h"
+#include <vector>
+#include <string>
+
+using namespace OpenMM;
+using namespace std;
+
+void testLoadNMLPlugin() 
+{
+    Platform::loadPluginsFromDirectory(Platform::getDefaultPluginsDirectory());
+    vector<string> kernelName;
+    kernelName.push_back("IntegrateNMLStepKernel");
+    // Was NormalModeLangevin plugin loaded?
+    const Platform& platform = Platform::findPlatform(kernelName); // throws if no platform with kernel
+}
+
+int main() 
+{
+    testLoadNMLPlugin();
+    return 0;
+}