Fixing broken links in doc, part 1: faq/
Fixing broken links in doc, part 2: howto/
Fixing broken links in doc, part 3: the rest
merge with 3.4
linkcheck: ignore issue URLs and PEP URLs (the latter until the PEPs are on www.python.org again).
Fixing broken links in doc, part 4: some more breaks and redirects
merge with 3.4