* don't need to provide values for all constants, just those required for model checking
And a few related bug fixes:
* in error handling for constants in PrismCL
* in export of labels from properties file with constants
And some small related API changes:
* don't need to call setUndefinedConstants on ModulesFile/PropertiesFile if there are no undefined constants
* more flexible UndefinedConstants classes
git-svn-id: https://www.prismmodelchecker.org/svn/prism/prism/trunk@3319 bbc10eb1-c90d-0410-af57-cb519fbb1720