gst/gst_private.h: add win32 specific import decoration(__declspec(dllimport)) for...

gst/gst_private.h: add win32 specific import decoration(__declspec(dllimport)) for all extern GstDebugCategory * vari...

Original commit message from CVS:
* gst/gst_private.h:
add win32 specific import decoration(__declspec(dllimport))
for all extern GstDebugCategory * variables
* win32/common/libgstbase.def:
* win32/common/libgstcontroller.def:
* win32/common/libgstreamer.def:
Add some exports, remove empty lines
* win32/common/libgstdataprotocol.def:
* win32/common/libgstdataprotocol.dsp:
* win32/common/libgstnet.def:
* win32/common/libgstnet.dsp:
new project files and exportation files added