[1.6.x] Fixed typo in multipartparser.py

Backport of 8a9d54aa69 from master
[1.6.x] Fixed #22579 -- Corrected validation for email to reject trailing slash

Backport of 424fe76349a2e34eafef13c2450a7a1f4d3115a6 from master.
[1.6.x] Fixed #22622 -- Added ugettext_lazy import in docs

Backport of 7271f5db78 from master
[1.6.x] Fixed #22167 -- Improved documentation on context processors

Backport of e7ffba8f78849fbf60b98fb8d67ef4577b585e3b from master.
[1.6.x] Fixed case in form widgets docs

Backport of 9494f29d from master
[1.6.x] Added stub release notes for 1.6.6.

Backport of 79e9da3d1e from master