sslutil: set `_canloaddefaultcerts` to `True` if `ssl.SSLContext` is present
The `load_default_certs()` method was already present when `ssl.SSLContext`
was backported to Python 2.7 (https://hg.python.org/cpython/rev/221a1f9155e2).
#require docutils gettext
Error: the current ro localization has some rst defects exposed by
moving pager to core. These two warnings about references are expected
until the localization is corrected.
$ $TESTDIR/check-gendoc ro
checking for parse errors
gendoc.txt:58: (WARNING/2) Inline interpreted text or phrase reference start-string without end-string.
gendoc.txt:58: (WARNING/2) Inline interpreted text or phrase reference start-string without end-string.