Do not fail homepage validation for 301 and 405.
Support other 30x status codes.
Do not follow redirects infinitely.
Merge branch 'master' into feature-allow-homepage-redirects

Conflicts:
	lib/cocoapods/validator.rb
Do not try to validate nil screenshots.
Keep houndci from barking.
Added Changelog entry.
Merge pull request #2027 from CocoaPods/feature-allow-homepage-redirects

Feature allow homepage redirects
Always try GET if HEAD fails when validating URLs.

Fixes problem in CocoaPods/Specs#10341