New drift and kick tasks in runner.c

src/part.h

@@ -32,8 +32,8 @@ struct xpart {
   /* Old position, at last tree rebuild. */
   double x_old[3];
 
-  /* Velocity at the half-step. */
-  float v_hdt[3];
+  /* Velocity at the last full step. */
+  float v_full[3];
 
   /* Entropy at the half-step. */
   float u_hdt;

src/space.c

@@ -1123,9 +1123,9 @@ void space_init(struct space *s, double dim[3], struct part *parts, int N,
   for (int k = 0; k < N; k++) {
     struct part *p = &parts[k];
     struct xpart *xp = &s->xparts[k];
-    xp->v_hdt[0] = p->v[0];
-    xp->v_hdt[1] = p->v[1];
-    xp->v_hdt[2] = p->v[2];
+    xp->v_full[0] = p->v[0];
+    xp->v_full[1] = p->v[1];
+    xp->v_full[2] = p->v[2];
     xp->u_hdt = p->u;
   }