Modified mist to accept the timeout as an optional argument:

I have modified the funcion 'mist_cmdline_options_handle'.
Now, this functions suppose that after the specification of the algorithm should appear the name of the file and that there is an optional argument 'timeout' that should appear followed by an integer which represent the timeout that the user wants to establish (in seconds).

I have also updated the function 'print_help'. I think that I did it wrong but I don't know how to specify that an argument is optional
Changed 'alarm' to 'setitimer' which counts only the time while the program is running instead of the wall clock time
Mist with the new check for petri nets works fine

I have also updated the Copyright
modified tree_dump to can use this function in is_petri_net. I have also modified all the ocurrences of tree_dump and call_back functions used with it
I think this is clearer
Fixed 'possible_petri_net' bug and some errors from my last commit

Fixed the bug about the possible/not possible constant values for the actions of a petri net.
Merge branch 'petri_net_checker'
branches merged