QUrl's constructor should accept strings without scheme as local paths

This piece of code:

QUrl u=QUrl::fromEncoded("/etc/passwd");
qDebug() << u.toLocalFile();

produces (as expected) "/etc/passwd" on Qt 4.7.x - on Qt 4.8.x, it produces ""

Qt5's QUrl constructor should work like Qt4's QUrl::fromEncoded, but it should decode strings without path as local files and set scheme() to "file".