Share some code between ctf and tfile target.

Share some code between ctf and tfile target.

This patch move the duplicated code between tfile and ctf
targets into file tracefile.c.  The common part of target_ops
fields are set in init_tracefile_ops.

gdb:

2014-02-23  Yao Qi  <yao@codesourcery.com>

	* ctf.c (ctf_has_stack, ctf_has_registers): Remove.
	(ctf_thread_alive, ctf_get_trace_status): Remove.
	(init_ctf_ops): Don't set some fields of ctf_ops.  Call
	init_tracefile_ops.
	* tracefile-tfile.c (tfile_get_trace_status): Remove.
	(tfile_has_stack, tfile_has_registers): Remove.
	(tfile_thread_alive): Remove.
	(init_tfile_ops): Don't set some fields of tfile_ops.  Call
	init_tracefile_ops.
	* tracefile.c (tracefile_has_stack): New function.
	(tracefile_has_registers): New function.
	(tracefile_thread_alive): New function.
	(tracefile_get_trace_status): New function.
	(init_tracefile_ops): New function.
	* tracefile.h (init_tracefile_ops): Declare.