Allow trailing newlines in receive-pack

Allow trailing newlines in receive-pack

C git's receive-pack.c strips trailing newlines in command lists when
present[1], although send-pack.c does not send them, at least in the
case of command lists[2]. Change JGit to match this behavior.
Add tests.

This also fixes parsing of commands in the push cert, which, unlike
commands sent in the non-push case, always have trailing newlines.

[1] https://github.com/git/git/blob/7974889a053574e449b55ca543a486e38e74864f/builtin/receive-pack.c#L1380
where packet_read_line chomps newlines:
https://github.com/git/git/blob/7974889a053574e449b55ca543a486e38e74864f/pkt-line.c#L202

[2] https://github.com/git/git/blob/7974889a053574e449b55ca543a486e38e74864f/send-pack.c#L470

Change-Id: I4bca6342a7482a53c9a5815a94b3c181a479d04b