TraitDictionary cleanup

Little bit of housekeeping for TraitDictionary in the first commit. Nothing worth calling out.

I discovered the All and GetMultiple methods for TraitContainer were being called enough to make a hand-rolled enumerator somewhat worthwhile.

For All, I saw CPU spent in enumeration drop by half from 1.90% to 0.94% of overall CPU time (measured on the RA shellmap for 30 seconds or so), and a more modest 1.25% to 1.00% change for GetMultiple. Not sure it's worth the extra code though so I'll let you chaps decide on that one.