Improved the reliability of CPBrowserCSSProperty by checking for the browser prefix *before* hyphenating the camel-cased string.

 This has the added benefit of ignoring unknown/unsupported prefixes, providing the property itself is camel-cased.

For example:

"LinearBackground" -> "linear-background"
"Linear-Background" -> "linear-background"
"linear-background" -> "linear-background"
"fooLinearBackground" -> "linear-background"

and

"WebkitLinearBackground" -> "-webkit-linear-background"
"MozLinearBackground" -> "-moz-linear-background"
etc..