closed #24 switched HudsonTestCase (junit3) to JenkinsRule (junit4).
refs #24 failed to add subclass of JenkinsRule.
refs #25 accept non-string list for SystemGroovyChoiceListProvider.
refs #25 documentation for SystemGroovyChoiceListProvider.
use same files for help for defaultChoice.
refs #25 added feature to test the script in configuration page.
closed #25 added tests for SystemGroovyChoiceListProvider#doTest and behavior for a non-string list value.