Add/remove issue watchers via the REST API (#6727).

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@11290 e93f8b46-1217-0410-a6f0-8f06a7374b81
Code cleanup.

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@11291 e93f8b46-1217-0410-a6f0-8f06a7374b81