Made the default GF implementation aring-m2-gf.  Moved, deleted unneeded code.
determinant via LU for RRR and CCC
Added/fixed promotions {RR,RRR}—>RR,RRR,CC,CCC, {CC,CCC}—>CC,CCC
Added some lift functions for RR,RRR—>{RR,RRR,CC,CCC}, and CC,CCC->CC,CCC.
EngineTest cleaned up; nullspaceU phased out
More linear algebra over fields work, part n.
fixed: clean, norm now work for matrices, mutable matrices and poly rings

over RR, CC fields.
LU decomp for RR,CC now go through mat-DU-template.
Fix a bug introduced in commit e4d1989.

The problem: polynomial rings over RR or CC also have precision, but
the standard division doesn’t work.  In fact, over poly rings, the
LU routines should NOT be used anyway…
Merge remote-tracking branch 'remotes/mike/linalg' into fastlinearalgebra.update-libraries.proposal