Description
mixed 
xdiff_string_merge3 ( string str1, string str2, string str3 [, string &error] )
     xdiff_string_merge3() merges strings 
     str1, str2 and 
     str3 into one.
    
     If error is passed then rejected parts are stored
     inside this variable.
    
     Returns merged string, FALSE if an internal error happened, or TRUE
     if merged string is empty.
    
     See also xdiff_file_merge3().