regcomp.c: Make sure optimizer handles node; Note for 3018b823

regcomp.c: Make sure optimizer handles node; Note for 3018b823

The check that there isn't a simple regnode unknown to the optimizer
has been commented out since at least
653099ff2c52a6af02b3894d684593dfe31dcc17 in 1999.  This caused us some
slow down for a while in the 5.17 release, as I added a regnode and
didn't think about it needing to be added to the optimizer.  This commit
uncomments out the check, but only for debugging builds, so that a
production environment will run with missing optimization, but
developers will be notified of their error.

Also, in commit 3018b823898645e44b8c37c70ac5c6302b031381, I made an
error in the commit message; I'm adding it here so people digging will
find out the relevant information.  The message said that the new regex
ops were unknown to the optimizer.  I had forgotten that I had included
them in that commit, so that statement was wrong.