respect XDG_CONFIG_HOME for getting user config dir.

Under linux the XDG Base Directory Specification define different
enviroment variables where to store what.
Log: Don't override level for csync

The level shall be set from Folder or owncloudCmd only.
Merge remote-tracking branch 'respect-XDG_CONFIG_HOME' into 1.5
HACK to avoid continuation: See task #1448

We do not know the _modtime from the server, at this point, so just set
the current one.  (rather than the one locally)
merged 1.5 into master