added info about the user space stream context for pipes

Author: weltling

UPGRADING

@@ -570,6 +570,13 @@ Other
     and ReflectionFunctionAbstract::getReturnType() methods both return an
     instance of ReflectionType.
 
+- Stream:
+  . New Windows only stream context options was added to allow blocking reads
+    on pipes. To enable it, pass array("pipe" => array("blocking" => true))
+    when creating the stream context. Be aware, that this option can under
+    circumstances cause dead locks on the pipe buffer. However it can be useful
+    in several CLI use case scenarios.
+
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 3. Changes in SAPI modules
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