REST API: custom fields definition (#11159).

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@12165 e93f8b46-1217-0410-a6f0-8f06a7374b81
AJAX call on the issue form resets data entered during the call (#14621).

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@12166 e93f8b46-1217-0410-a6f0-8f06a7374b81