1.0dev: fix saving //Comments only// pref in ticket view.
1.0dev: fix saving //Comments only// pref in ticket view.

`jQuery.ajax` doesn't send `undefined` value in `data`, which is what
`attr('checked')` returns when the checkbox is unchecked.
So we have to cast it to bool.


git-svn-id: eda3d06fcef731589ace1b284159cead3416df9b@11099 af82e41b-90c4-0310-8c96-b1721e28e2e2

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