gst/gstregistrybinary.*: Remove unnecessary <sys/mman.h> include which broke the win32 build with MingW; move include...

Original commit message from CVS:
* gst/gstregistrybinary.c: (gst_registry_binary_write_cache),
(gst_registry_binary_read_cache):
* gst/gstregistrybinary.h:
Remove unnecessary <sys/mman.h> include which broke the win32 build
with MingW; move includes from header file to .c file, even if the
header file isn't installed; use g_strerror() where UTF-8 strings
are expected, such as in GST_DEBUG messages.