Blender Git Loki

Making hash storage optional.

This required quite a bit of work, but storing hashes for 'simple' very quick
hashing/comparison functions is stupid (loss of space, and even introduces a
very small slow down), while with e.g. strings (which comparison and hasing
is quite expansive), it gives huge speedup (twice quicker insertion, about
33% quicker on lookup).

This makes lower-level code a bit less clear, since we add one 'child type' of Entry
for each case (GHash/GSet, and storing hash or not), but this also has the benefit
of being stricter when accessing entries' members...