Strip port numbers from HTTP host headers before comparing them for cookie purposes

Summary:
Browsers send port numbers (like ":443" or proxy ports) in the Host header and
we'll currently reject them with a message like:

Blah is configured on "x.y.com" but you are accessing it on "x.y.com:443".

Instead, examine only the host part.

Test Plan: Had my local listen on port 81 and accessed Phabricator before/after
the change; it now works without throwing.

Reviewers: jungejason, tuomaspelkonen, aran

Reviewed By: jungejason

CC: aran, epriestley, abdul, jungejason

Differential Revision: 841