updated vehicle dragging

rebalanced hauling pain penalty and gave a stamina discount to dragging wheeled vehicles

src/game.cpp

@@ -8909,7 +8909,13 @@ bool game::walk_move( const tripoint &dest_loc )
         Monsters don't currently have stamina however.
         For the time being just don't burn players stamina when mounted.
         */
-        u.burn_move_stamina( previous_moves - u.moves );
+        if( grabbed_vehicle == nullptr || grabbed_vehicle->wheelcache.empty() ) {
+            //Burn normal amount of stamina if no vehicle grabbed or vehicle lacks wheels
+            u.burn_move_stamina( previous_moves - u.moves );
+        } else {
+            //Burn half as much stamina if vehicle has wheels, without changing move time
+            u.burn_move_stamina( 0.50 * ( previous_moves - u.moves ) );
+        }
     }
     // Max out recoil
     u.recoil = MAX_RECOIL;

src/grab.cpp

@@ -120,11 +120,11 @@ bool game::grabbed_veh_move( const tripoint &dp )
         ///\EFFECT_STR increases speed of dragging vehicles
         u.moves -= 100 * str_req / std::max( 1, u.get_str() );
         const int ex = dice( 1, 3 ) - 1 + str_req;
-        if( ex > u.get_str() ) {
+        if( ex > u.get_str() + 1 ) {
             add_msg( m_bad, _( "You strain yourself to move the %s!" ), grabbed_vehicle->name );
             u.moves -= 200;
             u.mod_pain( 1 );
-        } else if( ex == u.get_str() ) {
+        } else {
             u.moves -= 200;
             add_msg( _( "It takes some time to move the %s." ), grabbed_vehicle->name );
         }