Merge doc changes from 3.2 (#8617, #10745).

In the install and library docs, I changed the text to refer to
packaging instead of distutils.  I also checked that the documented
paths correctly reflect what’s really defined in sysconfig; the main
difference with paths defined in distutils.install is that include
directories don’t end with the distribution name anymore (i.e. distutils
uses include/python3.3/spam, sysconfig include/python3.3), I have no
idea why.
diff --git a/Doc/using/cmdline.rst b/Doc/using/cmdline.rst
index 29c5772..f7bd92b 100644
--- a/Doc/using/cmdline.rst
+++ b/Doc/using/cmdline.rst
@@ -229,7 +229,8 @@
 
 .. cmdoption:: -s
 
-   Don't add user site directory to sys.path
+   Don't add the :data:`user site-packages directory <site.USER_SITE>` to
+   :data:`sys.path`.
 
    .. seealso::
 
@@ -470,7 +471,8 @@
 
 .. envvar:: PYTHONNOUSERSITE
 
-   If this is set, Python won't add the user site directory to sys.path
+   If this is set, Python won't add the :data:`user site-packages directory
+   <site.USER_SITE>` to :data:`sys.path`.
 
    .. seealso::
 
@@ -479,7 +481,10 @@
 
 .. envvar:: PYTHONUSERBASE
 
-   Sets the base directory for the user site directory
+   Defines the :data:`user base directory <site.USER_BASE>`, which is used to
+   compute the path of the :data:`user site-packages directory <site.USER_SITE>`
+   and :ref:`Packaging installation paths <packaging-alt-install-user>` for
+   ``pysetup run install_dist --user``.
 
    .. seealso::