Wrapped _preloaded_ssl_context with function to speed up package import

[gregory-shklover]

Wrapped around default SSL context initialization to potentially speed up "import requests" time.

Measurements:

original

$ time python -c "import requests" real 0m0.936s user 0m0.000s sys 0m0.047s

modified:

$ time python -c "import requests" real 0m0.351s user 0m0.000s sys 0m0.047s