gnu-nat.c: Don't install a deprecated_xfer_memory method.

gnu-nat.c: Don't install a deprecated_xfer_memory method.

This removes another instance of a deprecated_xfer_memory user.

gdb/
2013-09-19  Pedro Alves  <palves@redhat.com>
	    Thomas Schwinge  <thomas@codesourcery.com>
	    Yue Lu  <hacklu.newborn@gmail.com>

	* gnu-nat.c (gnu_read_inferior, gnu_write_inferior): Make static.
	Take a gdb_byte pointer instead of a char pointer.

	* gnu-nat.c (gnu_xfer_memory): Adjust interface as
	gnu_xfer_partial helper.
	(gnu_xfer_partial): New function.
	(gnu_target): Don't install a deprecated_xfer_memory hook.
	Install a to_xfer_partial hook.