[1.7.x] Fixed typo in docs/ref/request-response.txt

Backport of adf8fb34ce from master
[1.7.x] Fixed versionchanged indentation in topics/testing/advanced.txt.

Backport of 1387c80643 from master
[1.7.x] Replaced dead links to python-distribute.org.

Backport of dc241fdfdf from master