macro engine shouldn't allow private methods to leak into macro expansions

[scabug]

import scala.reflect.makro.Context

object Macros {
  private def veryPrivate = println("secrets leaked!!!")

  def impl(c: Context) = c.reify(veryPrivate)

  def foo = macro impl
}

object Test extends App {
  Macros.foo
}

Test_2.scala:2: error: method veryPrivate in object Macros cannot be accessed in object Macros
  Macros.foo
         ^
one error found

[scabug]

Imported From: https://issues.scala-lang.org/browse/SI-5755?orig=1
Reporter: @xeno-by
Affected Versions: 2.10.0-M3
Duplicates #8066

[scabug]

@xeno-by said:
We should have a special check for that, akin to the free terms / free types check.

[scabug]

@xeno-by said:
Duplicated by #8066