to Fiddle::Handle.
* ext/fiddle/pointer.c: Make Fiddle independent of DL, copy
  DL::Pointer to Fiddle::Pointer.
* test/fiddle/test_func.rb: relevent tests
* test/fiddle/test_handle.rb: ditto
* test/fiddle/test_pointer.rb: ditto
* ext/dl/lib/dl/struct.rb: use Fiddle::Pointer if available
* ext/fiddle/extconf.rb: check for dlfcn.h
* ext/fiddle/fiddle.c: add constants for sizeof() things
* ext/fiddle/fiddle.h: include dlfcn.h
* ext/fiddle/function.c: expose a C function for creating new
  Fiddle::Function objects.
* ext/fiddle/lib/fiddle.rb: include constants for dl backwards compat
* ext/fiddle/lib/fiddle/function.rb: read the pointer from the
  function for dl backwards compat.
* test/dl/test_callback.rb: check the addresses of the pointers rather
  than their types.
* test/fiddle/helper.rb: remove dependency on dl
* test/fiddle/test_closure.rb: ditto
* test/fiddle/test_fiddle.rb: ditto

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@37907 b2dd03c8-39d4-4d8f-98ff-823fe69b080e