Fixed ModuleInfo generation to no longer use the ModuleInfo class' default initializer for types/defaults, it's unsafe as initializers don't necesarily match the "formal" type. There might be explicit padding. Changed -g switch to emit DW_LANG_D debug info, make demangling work with a patched GDB, still more work to do for full support of D's Dwarf extensions. Added getNullValue helper method.

module aa4;

void main()
{
    int[int] aa;
    aa = addkey(aa,42,12);
    int* p = haskey(aa,42);
    assert(p && *p == 12);
}

int[int] addkey(int[int] aa, int key, int val)
{
    aa[key] = val;
    return aa;
}

int* haskey(int[int] aa, int key)
{
    return key in aa;
}