Allow loading of external scripts

External scripts weren't being loaded.  This patch respects the 'src' attribute on script elements within $dataContent, allowing external scripts to load.  This introduces a problem, however, since dynamically inserted external scripts load asynchronously. If scripts within $dataContent are order-dependent, this causes problems when the page is ajaxified, since there is no execution-order guarantee for these scripts. By setting 'scriptNode.async = false;' when this attribute isn't specified as true explicitly, dynamically inserted script nodes can be made to execute in-order (while still loading asynchronously). See http://wiki.whatwg.org/wiki/Dynamic_Script_Execution_Order.