this value is was chosen to exactly replicate `flow`'s behavior. IMO,
it would be less surprising to set the default to `1`, i.e., the user
needs to specify `--threads-per-process=$N` explicitly if
multithreaded linearization ought to be used.
this avoids regressions for decks that use well testing and makes
`ebos` work as expected if UMFPACK is not available, but obviously it
will not work for decks that use multisegment wells in earnest.
`flow` is unaffected by this because it does not use this type tag.
this is part of the release maintainance. in this context "core
headers" means the ones which do not include the well model headers,
and only those which are concerned with non-exotic functionality,
e.g., the PolyhedralGrid and ALUGrid vanguards are not changed.
This enables `ebos` to run Norne and other non-trivial data
sets. While at it, adapt the tolerances by `ebos`.
This patch only affects the research simulator, i.e. `flow` is
unaffected by it.
