[GH #175] Slightly reorganise current and add new sort benchmarks

These patches do some slight reorganisation of the existing sort benchmarks and add two new sort benchmarks: one for ResizableIntegerArray and one for ResizableFloatArray.

Here are the timing results on my Debian wheezy (amd64) system (Intel(R) Core(TM)2 Duo CPU T8300 @ 2.40GHz), just in case anyone's interested:

<pre>
time ./parrot examples/benchmarks/sort_ffa.pir
Sorted 1000000 floats

real 	0m0.797s
user	0m0.704s
sys	0m0.028s

time ./parrot examples/benchmarks/sort_fia.pir
Sorted 1000000 integers

real	0m0.666s
user	0m0.648s
sys	0m0.020s

time ./parrot examples/benchmarks/sort_rfa.pir
Sorted 1000000 floats

real	0m0.730s
user	0m0.704s
sys	0m0.020s

time ./parrot examples/benchmarks/sort_ria.pir
Sorted 1000000 integers

real	0m0.754s
user	0m0.680s
sys	0m0.020s
</pre>