Adds a 'Create and continue' button on the new issue form, that will create...

Adds a 'Create and continue' button on the new issue form, that will create the issue and display the form again (#2523).

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@2265 e93f8b46-1217-0410-a6f0-8f06a7374b81