Require is supposed to include each file only once, but if the same physical 
file is accessed from different paths, it can get included multiple times. Is 
this the correct behaviour?

Example 1

File a.rb
	puts "a includes b"
	require "b.rb"
	puts "a includes c"
	require "c.rb"

File b.rb
	puts "b includes c"
	require "c.rb"

File c.rb
	puts "C INCLUDED"

$ ruby a.rb
	a includes b
	b includes c
	C INCLUDED
	a includes c

C included once.

Example 2:

Change file b.rb
	puts "b includes c"
	require "./c.rb"

$ ruby a.rb
	a includes b
	b includes c
	C INCLUDED
	a includes c
	C INCLUDED

File c.rb is included twice.