test_requests: Add tests for morsel_to_cookie

These tests will ensure my changes to how we handle 'expires' don't cause any regressions.
cookies: Replace type checks with try/except
AUTHORS: Take credit
cookies: Take a less cowardly approach

Per discussion with @sigmavirus24, we'll take the less cowardly approach here.
"the RFC defines the Expires header as a string with the format we're assigning to ``time_template`` so checking if it is a string is unnecessary."

Crossing my fingers that this doesn't break anyones existing code...
cookies: Fix bugs found during CI
test_requests: convert tests to py.test style
Merge pull request #1772 from mdbecker/make_morsel_to_cookie_more_pythonic

Make morsel_to_cookie more pythonic