This is actually a very interesting question.
Usual approach is to use pattern matching on types but template
instance symbol is not a type on its own, it is just a symbol.
(with typeof == void)
My second guess was to check __traits(identifier, AliasParam) but
it looks like for aliased instance (contrary to aliased template
symbol) identifier is its mangled name.
I can't imagine really clean way to do it but comparing
__traits(identifier) to that specific mangled name can be a
reliable enough hack (better than stringof which has undefined
format).
