Function: addprimes
Section: number_theoretical
C-Name: addprimes
Prototype: DG
Help: addprimes({x=[]}): add primes in the vector x to the prime table to
 be used in trial division. x may
 also be a single integer. Composite "primes" are allowed,
 and in that case you may later get a message "impossible inverse", which
 will give you some factors. List the current extra primes if x is omitted. If
 some primes are added which intersect non trivially the existing table entries,
 suitable updating is done

