support for Opera browser

The Opera browser at version erlier than 15, was based
on Presto+Carakan engines, which followed the ECMA-262 Specification.
It requires a minimum of 2 parameters for a function
Date.UTC(year,month[,date[,hrs[,min[,sec[,ms]]]]]).
While the MUCkl script gave only 1 parameter, the Opera have always opened
a chatroom with error message
'Nickname is already in use by another occupant'.
The parameters for the Date.UTC() function has been fixed.