Remove useless walls.size() calls

Since we now have a reliable walls_num variable, replace walls.size()
with walls_num wherever possible.

functions.cpp

@@ -497,8 +497,8 @@ void reset(player& _player, e_list &enemies, boss& boss1, b_list& bullets, b_lis
 	
 	walls.resize(walls_num);
 
-	for(int i=0;i<walls.size();i++)
-		walls[i].create((i+1)*(C/(3*walls.size()+1))+i*(2*C/(3*walls.size()+1)),2*R/3,(int)min(6,2*C/(3*(int)(walls.size())+1)),2,5);
+	for(int i=0;i<walls_num;i++)
+		walls[i].create((i+1)*(C/(3*walls_num+1))+i*(2*C/(3*walls_num+1)),2*R/3,(int)min(6,2*C/(3*(int)(walls_num)+1)),2,5);
 	
 }
 	

invaders.cpp

@@ -117,7 +117,7 @@ int main(int argc,char** argv)
 	
 	int i=0;
 	for(w_vec::iterator it=walls.begin(); it!=walls.end(); ++it, ++i)				//creating walls (in a quite symmetric pattern)
-		it->create((i+1)*(C/(3*walls.size()+1))+i*(2*C/(3*walls.size()+1)),2*R/3,(int)min(6,2*C/(3*(int)(walls.size())+1)),2,3);
+		it->create((i+1)*(C/(3*walls_num+1))+i*(2*C/(3*walls_num+1)),2*R/3,(int)min(6,2*C/(3*(int)(walls_num)+1)),2,3);
 
 	/////////ENTERING MAIN LOOP