fetch: send server options when using protocol v2

fetch: send server options when using protocol v2

Teach fetch to optionally accept server options by specifying them on
the cmdline via '-o' or '--server-option'.  These server options are
sent to the remote end when performing a fetch communicating using
protocol version 2.

If communicating using a protocol other than v2 the provided options are
ignored and not sent to the remote end.

Signed-off-by: Brandon Williams <bmwill@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>