Reinstate "regcomp.c: Move 2 hdr inversion fields to SV hdr"

Reinstate "regcomp.c: Move 2 hdr inversion fields to SV hdr"

This reverts commit 67434bafe4f2406e7c92e69013aecd446c896a9a, which
reverted 4fdeca7844470c929f35857f49078db1fd124dbc, thus reinstating the
latter commit.  It turns out that the error being chased down was not
due to this commit.

Its original message was:

This commit continues the process of separating the header area of
inversion lists from the body.  2 more fields are moved out of the
header portion of the inversion list, and into the header portion of the
SV that contains it.