i#1439: Fix un-aligned special heap unit sizes (#3440)
i#1439: Fix un-aligned special heap unit sizes (#3440)

Fixes a bug where special heap units use an offset size for subsequent
units, resulting in wasted space as they leak a little bit onto an
additionally allocated page.

Adds ASSERTs on page alignment and confirmed that they show up in our
tests without this fix.

Fixes #1439

AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio