Release v1.0.1

The httpclient implementation keeps a `read_buf` that holds the data
in the body of the response after the headers have been written.  We
store that data for subsequent calls to `git_http_client_read_body`.  If
we want to stop reading body data and send another request, we need to
clear that cached data.

Clear the cached body data on new requests, just like we read any
outstanding data from the socket.

When `git_http_client_read_body` is invoked, it provides the size of the
buffer that can be read into.  This will be set as the parser context's
`output_size` member.  Use this as an upper limit on our reads, and
ensure that we do not read more than the client requests.

When users call `git_http_client_read_body`, it should return 0 at the
end of a message.  When the `on_message_complete` callback is called,
this will set `client->state` to `DONE`.  In our read loop, we look for
this condition and exit.

Without this, when there is no data left except the end of message chunk
(`0\r\n`) in the http stream, we would block by reading the three bytes
off the stream but not making progress in any `on_body` callbacks.
Listening to the `on_message_complete` callback allows us to stop trying
to read from the socket when we've read the end of message chunk.

Google Git (googlesource.com) behaves differently than git proper.
Test that we can communicate with it.

The `git_index_free()` merely decrement the reference counter from 2 to
1, and does not "free" the index.
Thus, the following `git_repository_index()` merely increase the counter
to 2, instead of read index from disk.
The written index is not read and parsed, which makes this test case
effectively becomes a no-op.

According to index-format.txt of git, the path of an entry is prefixed
with N, where N indicates the length of bytes to be stripped.