Removed the 'needsstorage' thing from Dsymbol. Arguments are not always given storage when applicable. This is not longer treat specially in this regard. Code for accessing nested variables and contexts rewritten. Probably more. Fairly well tested.

module bug1;
struct Foo { Foo opSub(ref Foo b) { return Foo(); } }
struct Bar { Foo whee; }
void test(ref Bar moo) { Foo nngh; auto plonk = nngh - moo.whee; }
void main() { Bar bar; test(bar); }