gc.collect(2) call shouldn't be forced by pandas
We have lots of objects allocated in memory and the explicit call to `gc.collect(2)` in `generic.py` is killing our app's performance (taking ~0.5s _each time_!)
https://github.com/pydata/pandas/blob/master/pandas/core/generic.py#L1278

Ideally pandas shouldn't call the garbage collector manually, or at the very list there should be a way to disable this call.

Thanks!
