* ./plugins/win32/win32.cpp: fixed `--intf intfwin' which wasn't working.

  * ./plugins/win32/win32.cpp: fixed `--intf intfwin' which wasn't working.
  * ./Makefile: we don't include the Gtk+ and SDL DLLs in the win32 package
    anymore, the package is now 700k instead of 4MB.
  * ./configure.in, ./Makefile, ./Makefile.opts.in: replaced LIB_FOO with
    foo_LDFLAGS and CFLAGS_BAR with bar_CFLAGS for faster builds, and moved a
    lot of stuff from Makefile.opts.in back to configure.in.
  * ./install-win32: updated script for NSIS 1.96.

   I hope this doesn't break too many other architectures...