Updated documentation of the shadow test.  Make it clear that
implementations are not allowed to use any source of information
other than /etc/shadow.  Also added reference to man page
shadow(5).
Merge pull request #145 from chisholm/master

Updated documentation of the shadow test.
Merge branch 'master' of https://github.com/OVALProject/Language
removing some smart quotes and long hypens.
Merge branch 'master' of https://github.com/OVALProject/Language
Merge branch 'master' of https://github.com/OVALProject/Language