D hash table comparison benchmark

[Nathan S.]

With LDC2 the times for vibe.utils.hashmap and memutils.hashmap 
are suspiciously low, leading me to suspect that the optimizer 
might be omitting most of the work. Here are the figures without 
optimizations enabled.

== Speed Ranking using DMD (no optimizations) ==
  95 msecs built-in AA
168 msecs vibe.utils.hashmap
182 msecs jive.map
224 msecs memutils.hashmap
663 msecs containers.hashmap w/GCAllocator
686 msecs containers.hashmap w/Mallocator

== Speed Ranking using LDC2 (no optimizations) ==
  68 msecs built-in AA
143 msecs vibe.utils.hashmap
155 msecs jive.map
164 msecs memutils.hashmap
515 msecs containers.hashmap w/GCAllocator
537 msecs containers.hashmap w/Mallocator