SECURITY: Make Special:MyPage and friends fake redirect to prevent info leak

SECURITY: Make Special:MyPage and friends fake redirect to prevent info leak

This prevents a malicious person from using external resources on their
website to cause the victim's web browser to load
Special:MyPage -> User:Username, and then looking it up in the page hit
statistics in order to correlate IPs from the malicious person's server
log, with usernames on wiki.

This feature can be disabled with $wgHideIdentifiableRedirects.

Bug: T109724
Signed-off-by: Chad Horohoe <chadh@wikimedia.org>
Change-Id: Ia0e742dc92c77af4832174dfa24c6dcaa6ee80e9