Fix HashMap when keys are objects that may override toHash and/or opEquals
Fix HashMap when keys are objects that may override toHash and/or opEquals

Includes a unittest demonstrating code that fails without this patch.

chalucha/vibe.d,rejectedsoftware/vibe.d,etcimon/vibe.d,etcimon/vibe.d,Geod24/vibe.d,gedaiu/vibe.d