new alarm GP function

[Bill Allombert <Bill.Allombert@math.u-bordeaux1.fr>]

Dear PARI users,

I just added the function alarm to GP (svn branch),

alarm({s = 0}):

   trigger an alarmer exception after s seconds,  cancelling any previously set
alarm. Stop a pending alarm if s = 0 or is omitted.

   For  example,   the  function timefact(N,sec) below will try to factor N and
give up after sec seconds, returning a partial factorisation.

default(factor_add_primes,1);
default(primelimit,16777216);
timefact(N,sec)=
{
  trap(alarmer,0,alarm(sec);factor(N);alarm(0));
  factor(N,16777216);
}

Cheers,
Bill.