git-svn: don't append extra newlines at the end of commit messages.

git-svn: don't append extra newlines at the end of commit messages.

In git, all commits end in exactly one newline character.  In svn, commits
end in zero or more newlines.  Thus, when importing commits from svn into
git, git-svn always appends two extra newlines to ensure that the
git-svn-id: line is separated from the main commit message by at least one
blank line.

Combined with the terminating newline that's always present in svn commits
produced by git, you usually end up with two blank lines instead of one
between the commit message and git-svn-id: line, which is undesirable.

Instead, let's remove all trailing whitespace from the git commit on the way
through to svn.

Signed-off-by: Avery Pennarun <apenwarr@gmail.com>
Acked-by: Eric Wong <normalperson@yhbt.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>