add context parameter to xmlrpclib.ServerProxy (#22960)

Patch from Alex Gaynor.

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extra : amend_source : c566176374a24dc5de60b1ac347d1f00893a4903
merge 2.7.9 release branch

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this is why tests are great

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merge 2.7.9 release branch

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backout fac649bf2d10 (#9179) for further consideration

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merge 2.7.9 release branch

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branch : 2.7