scm: darcs: add compatible test of Darcs 2.3 and 2.4.
git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/branches/1.1-stable@4750 e93f8b46-1217-0410-a6f0-8f06a7374b81
scm: darcs: change io.gets to io.read and add darcs version unit test.
git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/branches/1.1-stable@4746 e93f8b46-1217-0410-a6f0-8f06a7374b81