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

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.