* ./plugins/win32/intfwin.bpr: we now build intfwin.so at the right place.

  * ./plugins/win32/intfwin.bpr: we now build intfwin.so at the right place.
  * ./plugins/win32/Makefile: intfwin.so can be built using commandline.
  * ./configure.in, ./include/threads.h, ./include/common.h: a custom defs.h
    file isn't needed for the intfwin plugin anymore.
  * ./INSTALL.win32: updated compilation instructions for the intfwin plugin.