support for Opera browser

Opera browser before version 15, based on Presto+Carakan engines,
follow the ECMA-262 Specification, which allows minimum of 2 parameters
for a function Date.UTC(year,month[,date[,hrs[,min[,sec[,ms]]]]]).
When MUCkl gave only 1 parameter, Opera have started chatroom with error message
'Nickname is already in use by another occupant'.
The arguments for function Date.UTC() has been fixed.