ticket: Show a warning instead of an error when a workflow action is not available, and mention a concurrent editing warning if this is the cause.
ticket: Show a warning instead of an error when a workflow action is not available, and mention a concurrent editing warning if this is the cause.

Closes #8235.


git-svn-id: eda3d06fcef731589ace1b284159cead3416df9b@9443 af82e41b-90c4-0310-8c96-b1721e28e2e2

jun66j5/trac-ja,netjunki/trac-Pygit2,walty8/trac,jun66j5/trac-ja,walty8/trac,walty8/trac,jun66j5/trac-ja,netjunki/trac-Pygit2,netjunki/trac-Pygit2,jun66j5/trac-ja,walty8/trac