gst/gst_private.h: add a new #ifdef to use __declspec(dllimport) only for other modul...

gst/gst_private.h: add a new #ifdef to use __declspec(dllimport) only for other modules and not for gstreamer core

Original commit message from CVS:
* gst/gst_private.h:
add a new #ifdef to use __declspec(dllimport) only for
other modules and not for gstreamer core
* gst/gstbasesink.c: (gst_base_sink_perform_qos):
use gst_guint64_to_gdouble for conversion
* win32/common/libgstreamer.def:
add new exported functions
* win32/vs6/gst_inspect.dsp:
* win32/vs6/gst_launch.dsp:
* win32/vs6/libgstbase.dsp:
* win32/vs6/libgstcontroller.dsp:
* win32/vs6/libgstcoreelements.dsp:
* win32/vs6/libgstdataprotocol.dsp:
* win32/vs6/libgstnet.dsp:
update project files