Fix syncing a folder with '#' in the name

Or an url with '#'

Fixes #1838

The problem is a bug fixed in Qt5 now breaks.
In Qt4, QUrl::setPath() did not properly handle path with '#' in them
and QUrl::toString would restitute the '#'.

But csync will blindly do  "uri + path" before passing the path to
VIO.  because csync_update has no idea that the VIO plugin need special
encoding, the encoding cannot be done there.  But csync_owncloud then
encodes the full path.  So if the uri contains '#', it must not be already
encoded or there will be two encoding.