Changes to ZZ/p flint: random numbers are different, but repeatable

display, eval uses balanced representation (about 0).  This matches
previous behavior.
One fix to get EngineTests to pass tests
Changed default GF code to flint: both "small" and "big"

depending on SizeLimit option.  The Strategy option can currently
be used to choose "Old", "New" (both engine defined types), "Givaro",
"Flint", "FlintBig".  These first three might go away soon.
Merge pull request #21 from DanGrayson/linalg

Linalg
change ConwayPolynomials package to use flint

The flint library contains the list of Conway polynomials, so we
can delete our copy of it and start using flint to get the polynomials.
Merge branch 'linalg' of github.com:MikeStillman/M2 into linalg