Unify AA value alignment to size_t.sizeof (fixes bug 8583)

Sets the alignment of values in both AA declarations (object and aaA)
to size_t.sizeof bytes, which fixes byValue range iteration on x64.
Add unit tests for bug 8583; restore 16-byte aligment on x64

This adds unit tests for the alignment fix to Slot, ensuring the two
declarations of an AA slot stay in sync. The 16-byte alignment rule for
x64 has been restored.
Merge pull request #386 from pearfalse/master

Explicitly set AA value alignment in slot to size_t.sizeof bytes (fixes bug 8583)