Preserve script node attributes.

Some sites such as Dropbox.com use attributes on script nodes to
define how they should be ran (or include non-js script nodes).

Previously, only the innerHTML and src attributes would be preserved,
often triggering errors or broken functionality.  This change
uses the cloneNode function to copy the node while preserving
all attributes.

cloneNode is not supported by FF before 13, so if legacy support is
desired an alternate solution will have to be found.