amend commit: Support large loose objects as streams

amend commit: Support large loose objects as streams

We need to validate the stream state after the InflaterInputStream
thinks the stream is done.  Git expects a higher level of service from
the Inflater than the InflaterInputStream usually gives, we need to
ensure the embedded CRC is valid, and that there isn't trailing
garbage at the end of the file.

Change-Id: I1c9642a82dbd76b69e607dceccf8b85dc869a3c1
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>