@watching is a stack of lists of constants being watched. For instance, if
parent.rb is autoloaded, the stack will look like [[Object]]. If parent.rb then requires
namespace/child.rb, the stack will look like [[Object], [Namespace]].
# File activesupport/lib/active_support/dependencies.rb, line 90
def initialize
@watching = []
@stack = Hash.new { |h,k| h[k] = [] }
end
