[FIX] report_webkit: Wrong Report template file path throws 'Coercing to Unicode' error : (Maintenance Case : 583490)
cf.  http://bazaar.launchpad.net/~openerp-dev/openobject-addons/7.0-opw-583490-rgo/revision/8519
[FIX] path declaration must be OS independant => use '/' as neutral path separator
[MERGE] [FIX] correct path for printing webkit reports on windows server, courtesy of Olivier Laurent (Acsone)