DataStruct vectors leak when iterating

[bp-kelley]

Describe the bug
The Vectors defined in DataStructs leak memory when using pythonic iterators.

This appears to be caused by a leak in the C++ IndexErrorException that isn't properly wrapped.
The solution appears to be a simple import of rdkit.rdBase which defines these properly

To Reproduce

from rdkit.DataStructs import SparseBitVect
# if you add the following there are no leaks
#from rdkit import rdBase
import random
s = SparseBitVect(2048)
bv = SparseBitVect(2048)
for i in range(100):
    s.SetBit(random.randint(0,2047))

while 1:
    l = list(s)

Expected behavior
No memory leaks