Merge from 3.2 - Issue9637 - Explain in getproxies_environment that…

Merge from 3.2 - Issue9637 - Explain in getproxies_environment that <scheme>_proxy environ variable case does not matter.

Doc/library/urllib.request.rst

@@ -124,10 +124,10 @@ The :mod:`urllib.request` module defines the following functions:
 .. function:: getproxies()
 
    This helper function returns a dictionary of scheme to proxy server URL
-   mappings. It scans the environment for variables named ``<scheme>_proxy``
-   for all operating systems first, and when it cannot find it, looks for proxy
-   information from Mac OSX System Configuration for Mac OS X and Windows
-   Systems Registry for Windows.
+   mappings. It scans the environment for variables named ``<scheme>_proxy``,
+   in a case insensitive approach, for all operating systems first, and when it
+   cannot find it, looks for proxy information from Mac OSX System
+   Configuration for Mac OS X and Windows Systems Registry for Windows.
 
 
 The following classes are provided: