SAK-30781 Improve error message. (sakaiproject#2215)

In SAK-13054 we limited aliases, but this means the error isn't always because you don't have permission.

site-manage/site-manage-tool/tool/src/bundle/sitesetupgeneric.properties

@@ -52,7 +52,7 @@ java.notaccess = You do not have permission to change the access to this site.
 java.alias.exists = Alias ''{0}'' already exists.
 java.alias.isinval = Alias ''{0}'' is invalid.
 java.alias.locked = Alias ''{0}'' is locked.
-java.addalias = You do not have permission to add alias.
+java.addalias = You do not have permission to add an alias or you can't use this alias.
 java.delalias = You do not have permission to remove alias ''{0}''.
 java.rosters = You do not have permission to link to course roster(s).
 java.hello = Hello,