Port Ceres to Windows

This is a preliminary, but full, port of Ceres to Windows.
Currently all tests compile and run, with only system_test
failing to work correctly due to a path issue.

Change-Id: I4152c1588bf51ffd7f4d9401ef9759f5d28c299c
diff --git a/include/ceres/jet.h b/include/ceres/jet.h
index 552df65..e94df5d 100644
--- a/include/ceres/jet.h
+++ b/include/ceres/jet.h
@@ -650,6 +650,10 @@
   typedef ceres::Jet<T, N> NonInteger;
   typedef ceres::Jet<T, N> Nested;
 
+  static typename ceres::Jet<T, N> dummy_precision() {
+    return ceres::Jet<T, N>(1e-12);
+  }
+
   enum {
     IsComplex = 0,
     IsInteger = 0,