Make ';' suppresion of output optional

[Fernando Perez]

We supress output when an input line ends with ';', in contrast to how python itself works. Make it possible for the user to optionally disable this.

The code is in prompts.py, around line 548 (as of 2010/01/19):

           # do not print output if input ends in ';'
           try:
               if self.input_hist[self.prompt_count].endswith(';\n'):
                   return
           except IndexError:
               # some uses of ipshellembed may fail here
               pass

Reported by Sage, for reference: http://trac.sagemath.org/sage_trac/ticket/6650.