Correct implementation and documentation of os.confstr. Add a simple test
case. I've yet to figure out how to provoke a None return I can test.
diff --git a/Doc/lib/libos.tex b/Doc/lib/libos.tex
index ebe3021..9ded3ae 100644
--- a/Doc/lib/libos.tex
+++ b/Doc/lib/libos.tex
@@ -1844,14 +1844,14 @@
string which is the name of a defined system value; these names are
specified in a number of standards (\POSIX, \UNIX{} 95, \UNIX{} 98, and
others). Some platforms define additional names as well. The names
-known to the host operating system are given in the
+known to the host operating system are given as the keys of the
\code{confstr_names} dictionary. For configuration variables not
included in that mapping, passing an integer for \var{name} is also
accepted.
Availability: Macintosh, \UNIX.
-If the configuration value specified by \var{name} isn't defined, the
-empty string is returned.
+If the configuration value specified by \var{name} isn't defined,
+\code{None} is returned.
If \var{name} is a string and is not known, \exception{ValueError} is
raised. If a specific value for \var{name} is not supported by the