Check that the end of the splines are continuous

Check that we are continuous to the second derivitive of the spline.
This doesn't allow d alpha/ dd to not be the same across the junction.
ie, it's overly conservative.  That's a fine starting assumption.

Change-Id: I927565229e26df07a5c8b085c9e97c55da82c28b
diff --git a/frc971/control_loops/drivetrain/BUILD b/frc971/control_loops/drivetrain/BUILD
index 7e78c72..2bad4d9 100644
--- a/frc971/control_loops/drivetrain/BUILD
+++ b/frc971/control_loops/drivetrain/BUILD
@@ -288,6 +288,7 @@
     hdrs = ["distance_spline.h"],
     deps = [
         ":spline",
+        "//aos/logging",
         "//frc971/control_loops:fixed_quadrature",
         "//third_party/eigen",
     ],
@@ -309,6 +310,7 @@
     deps = [
         ":distance_spline",
         "//aos/testing:googletest",
+        "//aos/testing:test_shm",
         "@com_github_gflags_gflags//:gflags",
     ] + cpu_select({
         "amd64": [