improve checking for non-supported browsers

[ray]

As far as I remember HTMLArea was designed to "degrade gracefully" to a normal textarea. However, at the moment

• there's JS errors all over the place because of references to object properties that are not defined due to a check for browser support only in one place
• the plugins are loaded, wasting bandwidth
• Safari falsely identifies itself as Gecko

[ray]

fixed rev [767]

[guest]

I want to select the textarea and give the tags Bold,Italics and Underline to the selcted text .For eg:- like this kind of a textarea

[ray]

Interesting idea, but this has nothing to do with the topic of this ticket and is IMHO by far not in the focus of Xinha development, at least not in near time