Stop unintended re-encoding of author names from UTF-8 to ASCII

To see the bug in action, use an author map with umlauts, e.g.

  nickname = Hällo Wörld from UTF-8 <mail@example.org>

and check "git log" after the conversion.

What is happening?
QByteArray "author" is first decoded as UTF-8 into a QString.
That QString is passed to QByteArray::append(const QString &)
which internally encodes the QString to ASCII byte data using
QString::toAscii().  "git fast-import" expects UTF-8 input
from us, so the original QByteArray with UTF-8 content is just
what we need.

Author: hartwork

src/repository.cpp

@@ -736,7 +736,7 @@ void Repository::Transaction::commit()
     QByteArray s("");
     s.append("commit " + branchRef + "\n");
     s.append("mark :" + QByteArray::number(mark) + "\n");
-    s.append("committer " + QString::fromUtf8(author) + " " + QString::number(datetime) + " +0000" + "\n");
+    s.append("committer " + author + " " + QString::number(datetime).toUtf8() + " +0000" + "\n");
     s.append("data " + QString::number(message.length()) + "\n");
     s.append(message + "\n");
     repository->fastImport.write(s);