In Scala there are some methods that only exist in symbol tables,
but don't have corresponding method entries in Java class files.

To the best of my knowledge, these methods can be subdivided into four groups:
1) stuff weaved onto Any, AnyVal and AnyRef,
2) magic methods that Scala exposes to fix Java arrays,
3) compile-time methods (such as classOf and all kinds of macros),
4) miscellaneous stuff (currently only String_+).

To support these magic symbols, I've modified the `checkMemberOf` validator
to special case Any/AnyVal/AnyRef methods and adjusted MethodMirror and
ConstructorMirror classes to use special invokers for those instead of
relying on Java reflection.

First of all in 911bbc4 I've completely overlooked the fact that
reflectConstructor exists and that is also needs sanity checks.

Now reflectConstructor checks that the incoming symbol is actually a ctor,
and that it is actually a ctor of the class reflected by the current mirror.

Secondly while fixing reflectConstructor I've found out that reflectXXX methods
don't accept inherited, but overriden members. That's also fixed now.

Haha that was a nice one. After a fixed the problem with inherited members,
I've uncovered another issue. If we have a field overriden in a descendant,
then (unlike with methods) overriding and overriden members make sense
independently of each other.

Hence in `FieldMirror.get` we need a way of specifying whether we want the base
value or the overriding value. To do that I introduced an optional parameter.
The same parameter has been added to `FieldMirror.set`. Despite the fact that
Scala currently doesn't normally allow to override vars (not counting the
-Yoverride-vars internal flag), I think, it's better to be forward-compatible,
since it induces zero usage overhead.