[with patch; needs work] modular forms -- add aplist and anlist for newforms

[cremona]

Looks mainly good to me -- patch applies and tests (in sage/modular/modform) pass. One glitch:

        if not all_embeddings: 
 	            return A 
 	return A 

looks like a typo.

It does not seem very efficient to factor all the n in the range, and that is not the way I have always done this. The result is pretty slow -- for example, if you wanted to compute all a_n for n<10^{6, this is not good enough:}

sage: f = CuspForms(11,2).newforms()[0]; f
q - 2*q^2 - q^3 + 2*q^4 + q^5 + O(q^6)
sage: time an = f.anlist(1000)
CPU times: user 0.40 s, sys: 0.00 s, total: 0.40 s
Wall time: 0.40 s
sage: time an = f.anlist(10000)
CPU times: user 13.84 s, sys: 0.79 s, total: 14.63 s
Wall time: 14.65 s
sage: time an = f.anlist(100000)
#(gave up waiting after a few minutes)

On second thoughts it is probably computing the a_p which is slow here. But are they even cached?

sage: time an = f.aplist(10000)
CPU times: user 11.09 s, sys: 0.65 s, total: 11.74 s
Wall time: 11.81 s
sage: time an = f.anlist(10000)
CPU times: user 13.71 s, sys: 0.69 s, total: 14.40 s
Wall time: 14.53 s

-- it seems not.