xwiki.properties do not split list valued properties if read from /etc/xwiki

If the property file is read in from /etc/xwiki/xwiki.properties then list valued properties, which are given as a CSV are not split into list elements. This mostly affects attachment.download.whitelist (if used).

Steps to reproduce:

• copy the xwiki.properties to /etc/xwiki (if this file does not already exists)
• uncomment the attachment.download.whitelist property and add application/pdf to the list of mime-types
• restart some XWiki instance and upload a PDF file with a user without programming rights
• download the PDF file; if the configuration works, you should be able to see it inline in the browser. Instead a download dialog appears.

As mostly installations from Debian packages might be affected, there is the following workaround:

• rename the /etc/xwiki/xwiki.preferences to something else
• change the symbolic link in /usr/lib/xwiki/WEB-INF/xwiki.properties to point to the renamed file.
  Of course this is not update safe; one need to change the symbolic link after each update.