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 foreach7;

void main()
{
    int[4] a = [1,2,3,4];
    int i;
    foreach(v; a[0..3])
    {
        i += v;
    }
    assert(i == 6);
}