!noexec option for scripts loaded by js! seems non-functional

[unscriptable]

The test for the !noexec option for the js! plugin seems broken.

[unscriptable]

!noexec option removed. The "text/cache" trick no longer works for this purpose. "text/cache" still works for prefetching in browsers that don't yet support async="false", though. It's just that all browsers that support async="false" seem to ignore script elements with unsupported script types (which is the same ting to do).

This feature could be implemented by using doc.createElement('object').onload if demand for !noexec emerges. (doc.createElement('image').onload causes the "sticky mime type" bug in Chrome, so it's not an option atm.)