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 .

// bug #191

int[3] a = [0: 0, 2: 42, 1: 1];

void main()
{
  assert(a[0] == 0);
  assert(a[1] == 1); // fails!
  assert(a[2] == 42);
}