[patch] "for e in getSTLLikeCollection()" crashes pyroot

In PyROOT, trying to iterate over a collection returned from a function can result in destruction of the collection before its iterators, e.g.

for elem in getset():

    print(elem)

will crash, whereas

s = getset()

for elem in s:

    print(elem)

, where s has a larger scope, will work as expected. (see attached test)

I was able to fix this by adding a _collection attribute to the iterator in StlSequenceIter(), which ensures the reference count for the collection cannot reach 0 before the iteration is finished.

std::vector is handled as a special case with its own iterator type by PyROOT and is not affected by this problem.