Allow initial load to be restored

[cobbdb]

After using disableInitialLoad, the site is locked down and all future calls must be made twice. This is dumb and I hate it. Expose option to restore initial load after the first ad call has returned.

// as-is currently
pubads().disableInitialLoad();
harmony.show(name); // nothing happens.
harmony.show(name); // first ad call goes out.

// ... sometime later
harmony.show(name); // nothing happens
harmony.show(name); // now the ad loads

// should be option to support:
harmony.disable.initialLoad(true);
harmony.show(name); // nothing happens.
harmony.show(name); // first ad call goes out.

// ... sometime later
harmony.show(name); // ad loads no fuss no muss