refine comment

The constructors in each object file get merged during linking
so it's better to speak of shared libraries and executables
instead of object files.
Fix bug 5842.

The bug is caused by rehash producing an AA with a zero-size hashtable
when called on an empty but non-null AA.
When AA is empty, rehash should revert it to original state.
Need to call GC.free on old table in AA rehash.
Merge pull request #556 from dawgfoto/refineComment

refine comment
Merge pull request #576 from quickfur/issue5842

Fix bug 5842.
Add forward range capability to AA .byKey and .byValue.
Merge pull request #582 from quickfur/aa_fwdrange

Add forward range capability to AA .byKey and .byValue