Refactor|Server: Use ThinkerT in the server delta pool

The delta pool will not have to worry about the private data pointers,
as the pool itself needs to be reimplemented to cooperate with DMU.
Therefore the pool can continue taking a straight up copies of mobjs.

doomsday/server/include/server/sv_pool.h

@@ -99,6 +99,8 @@ typedef mobj_t  dt_mobj_t;
 typedef struct mobjdelta_s {
     delta_t         delta; // The header.
     dt_mobj_t       mo; // The data of the delta.
+
+    mobjdelta_s() : mo(thinker_s::InitializeToZero) {}
 } mobjdelta_t;
 
 typedef struct {

doomsday/server/src/server/sv_pool.cpp

@@ -101,7 +101,7 @@ static float deltaBaseScores[NUM_DELTA_TYPES];
 
 // Keep this zeroed out. Used if the register doesn't have data for
 // the mobj being compared.
-static dt_mobj_t dummyZeroMobj;
+static ThinkerT<dt_mobj_t> dummyZeroMobj;
 
 /**
  * Called once for each map, from R_SetupMap(). Initialize the world
@@ -504,7 +504,7 @@ dd_bool Sv_RegisterCompareMobj(cregister_t *reg, mobj_t const *s, mobjdelta_t *d
 {
     int df;
     reg_mobj_t *regMo = 0;
-    dt_mobj_t const *r = &dummyZeroMobj;
+    dt_mobj_t const *r = dummyZeroMobj;
 
     if((regMo = Sv_RegisterFindMobj(reg, s->thinker.id)) != NULL)
     {