Provide redirection follow capabilities in HTTP API when safe_mode or open_basedir are set

[sivel]

When safe_mode or open_basedir are set it seems that the only transport that can "follow" the redirects is fsockopen. All others stop after the initial request.

Simplepie seems to have a method of "manually" following by checking to see if the last response was a 30x and checks the number of redirects. If the last response was a 30x and the redirects that happened were less than configured it does a "manual" follow by requesting, grabbing the 'Location' header and then requesting again until it either hits the redirect limit or a non 30x response code.

[sivel]

Just to cross reference 2 other tickets:
#10416
#10418

[dd32]

I believe one of the transports includes a check to see if its running under safemode, and not to use it in that scenario.

Just need some extra constraints added to the ::test(); methods IMO

[sivel]

Basically in the end if we add the checks to see if running in safe mode it will limit us to fsockopen. That is fine with me, if everyone else is ok with it.

[dd32]

See: #11305 WP_Http won't follow redirects if open_basedir is in effect