To do list
* p-adics
- #8241: p-adic fields should have Witt Frobenius
- #8685: evaluation of Monsky-Washnitzer objects (is really about power series over p-adics)
- #9887: Slow coercion from integer ring to integer mod ring
- #11319: Cannot create homomorphism from prime residue field to finite field
- #11777: Coercion/printing problem with p-adics
* computing with chi_18