Expand generic-parsing special cases to cover `>=` and `>>=`

[sp3d]

Right now we have a parser tweak so that closing two generics in a row without a space between > signs works fine. It would be nice if this also worked for closing generics immediately prior to an equals sign, as in the following example:

struct S<T>
{
    data: T,
}
static s1:S<S<uint>>=S { data: S {data: 0}};
static s2:S<uint>=S { data: 0};