Removes an unnecessary statement from gc mode.  The reference count does not
need to be set to zero during node allocation.

On yellow-eyed:
(Debug requires unlimited stack).

------ Config refcnt-opt ------
reverse              0:01.04
tak                  0:00.64
rfib                 0:00.15
exp3_8               0:00.20
tree_insert          0:00.42
tree_insert_32       0:00.42
------ Config gc-opt ------
reverse              0:00.65
tak                  0:00.60
rfib                 0:00.11
exp3_8               0:00.10
tree_insert          0:00.53
tree_insert_32       0:00.54
------ Config refcnt-dbg ------
reverse              0:15.59
tak                  0:07.14
rfib                 0:02.16
exp3_8               0:02.27
tree_insert          0:04.29
tree_insert_32       0:04.53
------ Config gc-dbg ------
reverse              0:07.73
tak                  0:03.58
rfib                 0:01.20
exp3_8               0:01.19
tree_insert          0:02.28
tree_insert_32       0:02.40
Changes scripts/bench to print the hostname.
Adds index (git diff sprite/lib/list.hpp) to the list library.  Adds the primes benchmark (works for gc; SEGVs for refcnt).
Adds missing files for previous commit.
Adds a new configuration for debugging optimized code.