Froyo InputStream.available documentation improvement.

Froyo InputStream.available documentation improvement.

This method causes a lot of confusion, and we can do a lot better. (Ideally,
the API would either not exist or be something like "public boolean ready()".)

I've removed poor-quality documentation overrides too, so the full
documentation is visible in most places. (InflaterInputStream is an obvious
exception.)

Also, to a lesser extent, improve the InputStream.skip documentation.

Change-Id: I6d6cd788e6a32ad4a2613d1e381610f1ad8575fe