Description:
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stream_context_set_default() doesn't publish the context to all PHP extension.

Example is ext/libxml that doesn't recognize the context.

Test script:
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stream_context_set_default(array('http'=>array('proxy'=>'my_proxy_url')));

$x = simplexml_load_file('http://some_resource');

Expected result:
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The resource gets loaded through the HTTP proxy

Actual result:
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The resource is not loaded through the HTTP proxy.
For this to work, we have to use :

$ctx = stream_context_create(array('http'=>array('proxy'=>'my_proxy_url')));
libxml_set_streams_context($ctx); // userland manual bind

$x = simplexml_load_file('http://some_resource');