Fix inline comments by converting to block comments.

With the existing implementation, a line-based inline comment (that starts with "//") preceded with js code will cause subsequent lines to be ignored (commented out) when joined to become a single line and sent to the inferior js process.  This patch lessens the problem by converting inline comments to block comments.

Note that this is not foolproof, e.g., in case the js code to be sent contains a string that contains the "//" substring.