Automatically send WYSIWYG browsers into source mode instead of refusing to work

[cobaltbluedw]

Browsers that don't support tag editing still support ckeditor's source mode, which is better than nothing, and provides a more gradual operational decline.

My suggested patch creates a env.isTextCompatible var, and if env.isCompatible is false but env.isTextCompatible is true, ckeditor defaults to a text entry mode with limited, but still existent functionality.

[cobaltbluedw]

diff on ckeditor trunk to add smooth compatibility degradation