Congratulations to all the Nim devs, RTree now works with --gc:arc!

[Stefan_Salewski]

Not only ~/Nim/tests/generics/trtree.nim but also the extended one with 
bulkloading and nearest neightbour search from 
[https://github.com/StefanSalewski/RTree](https://github.com/StefanSalewski/RTree).

And fully unchanged!

Running with valgrind we get
    
    
    $ nim c --gc:arc -d:useMalloc rtree.nim
    
    $ valgrind ./rtree
    
    ==14702== HEAP SUMMARY:
    ==14702==     in use at exit: 61,092,320 bytes in 157,909 blocks
    ==14702==   total heap usage: 339,133 allocs, 181,224 frees, 85,099,823 
bytes allocated
    ==14702==
    ==14702== LEAK SUMMARY:
    ==14702==    definitely lost: 30,410,976 bytes in 82,268 blocks
    ==14702==    indirectly lost: 30,681,344 bytes in 75,641 blocks
    
    
    Run

Is this something we should worry about? (There should be no cyclic references 
be involved.)