Remove flush() call in wp_cache_get_response_headers()

[zytzagoo]

For more details see: https://github.com/Automattic/wp-super-cache/issues/126

Fixes #126

[kraftbj]

At first read, your explanation and process makes sense to me. Donncha (primary dev) is on vacation and want to get his nod for modifying something this ancient ;-).

[donnchawp]

We should check it in BUT we'll have to modify it because for some reason apache_response_headers() doesn't always behave and needs flush() to do the job. See this comment for more details.

I'll check the headers and if it's empty I'll call flush() and get the headers again.

[DrLightman]

Buf flush() can't be used inside an output buffer display handler anyway, otherwise it triggers this PHP Fatal error:

PHP Fatal error: Unknown: Cannot use output buffering in output buffering display handlers in Unknown on line 0

Because flush() is used inside wp_cache_get_response_headers() that is used inside wp_cache_shutdown_callback() that is used inside wp_cache_ob_callback() that has been registered as an output callback handler with:

ob_start( 'wp_cache_ob_callback' );

[donnchawp]

Ah, you're right. Take a look at #196 - I removed the flush() and changed the flow of the code so that headers_list() is used if apache_response_headers() fails.