Adds explicit alignment information for alloca instructions in general, there's a few cases that still needs to be looked at but this should catch the majority. Fixes ticket #293 .

module aa2;

void main()
{
    long[float] aa;
    long* p = 2.0f in aa;
    assert(!p);
    aa[4f] = 23;
    p = 4f in aa;
    assert(p);
    assert(*p == 23);
}