Add target_ops argument to to_read_btrace

Add target_ops argument to to_read_btrace

2014-02-19  Tom Tromey  <tromey@redhat.com>

	* target.h (struct target_ops) <to_read_btrace>: Add argument.
	* target.c (struct target_ops) <to_read_btrace>: Add argument.
	* remote.c (struct target_ops) <to_read_btrace>: Add 'self'
	argument.
	* amd64-linux-nat.c (amd64_linux_read_btrace): New function.
	(_initialize_amd64_linux_nat): Use it.
	* i386-linux-nat.c (i386_linux_read_btrace): New function.
	(_initialize_i386_linux_nat): Use it.