[3.6] bpo-14826: document that URLopener quotes fullurl. (GH-12758)#12760

miss-islington wants to merge 1 commit intopython:3.6python/cpython:3.6from

miss-islington:backport-2fb2bc8-3.6miss-islington/cpython:backport-2fb2bc8-3.6Copy head branch name to clipboard