Log Message:
Changes 0.77:
* [no changes]

Changes 0.76_50:
* Split out HEK size calculation into hek_size(). Add the shared HE overhead.
* Handle shared hash key scalars correctly.
* GvNAME() is shared from 5.10 onwards.
* Count HvNAME(), the HV "aux" struct, the mro_meta struct, and ENAMEs.

Changes 0.76:
* Just fix the version number in the line below.