Raise error("interrupted!") when torch-qlua is interrupted by ctrl-C.

I modified torch-qlua to react to ctrl-C like torch-lua.

Example usage:

    $ torch-qlua -e 'while true do os.clock() end'
    ^Ctorch-qlua: interrupted!
    stack traceback:
    	[C]: ?
    	[C]: in function 'clock'
    	[string "while true do os.clock() end"]:1: in main chunk