Ng to win32

Hello,

Thanks to Gisle's efforts, libnetng is working under win32 with VC
supoprt, except for the 802.11 builder (because variadic macros are
not yet supoprted).

ng-050112
- more win32 fixes [GV]
    - LIBNET_API exports
    - libnet_mode_link_win32.c: wrong 'l->output' set after
      libnet_select_device()
    - libnet_win32.c: added front-ent for MSVC malloc-debugger in
      debug-builds; memdbg_init().
    - libnet-swab.h: ULL not defined with VC6
    - libnet_mode_link_win32.c: wrong 'l->output' set after
      libnet_select_device()
- struct libnet_802_11_mgmt_probe_req_hdr:  added a 'int dummy' as
  some compiler wont accept an empty structure
- libnet_context.c must always call l->op_close(l), thus changed the
  close op of each mode to handle that

http://www.security-labs.org/libnetng/

He is (probably) performing more tests, so an update has to be
expected soon.

Anyway, he greatly deserves the whisky I owe him !!!

	Fred