Make using new for allocating DF objects with vtables a compile-time …

…error.

When done from plugins, it doesn't correctly initialize the vtable
because of some weird things MSVC does, so the only safe way is to
use df::allocate<df::foo>(). For consistency, it is also enforced
for code in the main library. It reveals the issue in the digging
invaders plugin, first found by warmist.

This change is linked to a modification in df-structures codegen.

library/include/df/custom/viewscreen.methods.inc

@@ -0,0 +1 @@
+friend struct df::interfacest;

library/modules/Items.cpp

@@ -997,16 +997,22 @@ df::proj_itemst *Items::makeProjectile(MapExtras::MapCache &mc, df::item *item)
     if (!ref)
         return NULL;
 
+    auto proj = df::allocate<df::proj_itemst>();
+    if (!proj) {
+        delete ref;
+        return NULL;
+    }
+
     if (!detachItem(mc, item))
     {
         delete ref;
+        delete proj;
         return NULL;
     }
 
     item->pos = pos;
     item->flags.bits.in_job = true;
 
-    auto proj = new df::proj_itemst();
     proj->link = new df::proj_list_link();
     proj->link->item = proj;
     proj->id = (*proj_next_id)++;

plugins/diggingInvaders/assignJob.cpp

@@ -88,10 +88,10 @@ int32_t assignJob(color_ostream& out, Edge firstImportantEdge, unordered_map<df:
         df::job* job = new df::job;
         job->job_type = df::enums::job_type::DestroyBuilding;
         //job->flags.bits.special = 1;
-        df::general_ref_building_holderst* buildingRef = new df::general_ref_building_holderst;
+        df::general_ref_building_holderst* buildingRef = df::allocate<df::general_ref_building_holderst>();
         buildingRef->building_id = building->id;
         job->general_refs.push_back(buildingRef);
-        df::general_ref_unit_workerst* workerRef = new df::general_ref_unit_workerst;
+        df::general_ref_unit_workerst* workerRef = df::allocate<df::general_ref_unit_workerst>();
         workerRef->unit_id = firstInvader->id;
         job->general_refs.push_back(workerRef);
         getRidOfOldJob(firstInvader);
@@ -118,7 +118,7 @@ int32_t assignJob(color_ostream& out, Edge firstImportantEdge, unordered_map<df:
         if ( construction2 ) {
             df::job* job = new df::job;
             job->job_type = df::enums::job_type::RemoveConstruction;
-            df::general_ref_unit_workerst* workerRef = new df::general_ref_unit_workerst;
+            df::general_ref_unit_workerst* workerRef = df::allocate<df::general_ref_unit_workerst>();
             workerRef->unit_id = firstInvader->id;
             job->general_refs.push_back(workerRef);
             job->pos = pt2;
@@ -189,7 +189,7 @@ int32_t assignJob(color_ostream& out, Edge firstImportantEdge, unordered_map<df:
             job->pos = workHere;
             firstInvader->path.dest = goHere;
             location = goHere;
-            df::general_ref_unit_workerst* ref = new df::general_ref_unit_workerst;
+            df::general_ref_unit_workerst* ref = df::allocate<df::general_ref_unit_workerst>();
             ref->unit_id = firstInvader->id;
             job->general_refs.push_back(ref);
             firstInvader->job.hunt_target = NULL;