Fix mktime() overflow error in test_email: run
test_localtime_daylight_true_dst_true() and
test_localtime_daylight_false_dst_true() with a specific timezone.
(cherry picked from commit cfaafda8e3)
Co-authored-by: Victor Stinner <vstinner@redhat.com>
Without this function people would be tempted to use the other date functions
in email.utils to compute an aware localtime, and those functions are not as
good for that purpose as this code. The code is Alexander Belopolsy's from
his proposed patch for issue 9527, with a fix (and additional tests) by Brian
K. Jones.
