Unclear start conditions due to memory pollution

The simulation starts in unclear conditions as setupNodesAndTransistors function does not clear the memory it allocates, leading to odd results at times. This is not a problem for the MOS 6502 netlist as it does the RESET. But it can be suprising if netlist_sim is used independently.

[tom-seddon]

I had problems with this building with VC++, which fills newly-malloc'd memory with 0xcd. This caused some access violations due to out-of-range indexes. So I changed the code to use calloc,, which seemed to do the job: tom-seddon@4c166df

Runs fine like this on OS X too (and valgrind doesn't complain any more).

--Tom