select() incorrectly splits some selectors

[Kerry Kurian]

element.py:

1345 def select(self, selector, _candidate_generator=None, limit=None):
1346 """Perform a CSS selection operation on the current element."""
1347
1348 # Handle grouping selectors if ',' exists, ie: p,a
1349 if ',' in selector:
1350 context = []
1351 for partial_selector in selector.split(','):

The selector is split on comma irrespective of whether the comma is in quotes. This is problematic when the selector is something like the following:

    a[title="Houston, we have problem"]

In this example the selector is erroneously split into:

    'a[title="Houston'

and:

    ' we have problem"]'