Don't compare date and datetime.

A request has failed with the following information:
- code: GENERIC_EXCEPTION
- short message: Unknown error: can't compare datetime to date.
- stack: no stack
- message: Unknown error: can't compare datetime to date.
Traceback (most recent call last):
  File "/home/nferrari-kresus/www/app/build/server/weboob/main.py", line 669, in fetch
    results['values'] = self.get_operations(from_date)
  File "/home/nferrari-kresus/www/app/build/server/weboob/main.py", line 570, in get_operations
    if histop.rdate and histop.rdate > op_date:
TypeError: can't compare datetime to date

- stringified: {"code":"GENERIC_EXCEPTION","message":"Unknown error: can't compare datetime to date.\nTraceback (most recent call last):\n  File \"/home/nferrari-kresus/www/app/build/server/weboob/main.py\", line 669, in fetch\n    results['values'] = self.get_operations(from_date)\n  File \"/home/nferrari-kresus/www/app/build/server/weboob/main.py\", line 570, in get_operations\n    if histop.rdate and histop.rdate > op_date:\nTypeError: can't compare datetime to date\n","shortMessage":"Unknown error: can't compare datetime to date."}

We need to cast all dates to date objects (or to datetime) to compare dates (instead of keeping one to datetime);