More updates to benchmark infrastructure.

Highlights:
 * Make `update-counts.sh` script more robust.
 * Update `hamlet.sml` benchmark program to close input file after each loop.
 * Update `fft.sml` benchmark program to only invoke `test` function with power-of-2 arguments.
 * Update to `model-elimination.sml` benchmark program to iterate `main ()` according to `doit` size parameter.