gst/gstbin.h: Replace interface parameter name by iface as interface is a reserved keyword in Visual Studio for C++ p...

Original commit message from CVS:
* gst/gstbin.h:(gst_bin_get_by_interface),
(gst_bin_iterate_all_by_interface):
Replace interface parameter name by iface as interface is
a reserved keyword in Visual Studio for C++ projects so it removes
a build error for application developpers using VS.
* plugins/elements/gstfilesrc.c:(gst_file_src_uri_set_uri):
Fix a bug on Windows in uri format check. Now the prefix checked
is file:// and next we check if the path after file:// is absolute.
* win32/common/libgstbase.def:
* win32/common/libgstdataprotocol.def:
* win32/common/libgstgstreamer.def:
Add new exported functions.