Fix KUrl::isRelativeUrl to allow all RFC3986 characters in scheme.
Review Request #129208 - Created Oct. 17, 2016 and submitted
RFC3986 defines the following syntax for URI schemes scheme = alpha *( alpha | digit | "+" | "-" | "." ) The '.' was missing which leaded to the problem that xdg-open opc.tcp://localhost didn't work. Background: xdg-open calls kde-open which then uses KUrl and so leaded to this problem. Of course this bug may affect also many other locations using KUrl::isRelativeUrl. This fix also adds a unit test to test the fix and avoid future regressions.