Change the default implementation of to_traceframe_info to tcomplain

This patch is to change the default implementation of to_traceframe_info
from 'return NULL' to tcomplain, which is intended.  If new target
supports tracepoint, this method should be implemented, otherwise,
an error is thrown.

gdb:

2014-03-06  Yao Qi  <yao@codesourcery.com>

	* target.h (struct target_ops) <to_traceframe_info>: Use
	TARGET_DEFAULT_NORETURN (tcomplain ()).
	* target-delegates.c: Regenerated.
Fix PR16508

This patch fixes PR16508, which is about MI "-trace-find frame-number 0"
behaves differently from CLI "tfind 0".  In CLI, we check both
status->running and status->filename, but in MI, we only check
status->running, which looks wrong to me.  This patch moves the code
of checking to a new function check_trace_running, and use it in
both CLI and MI.

This patch also adds a test case pr16508.exp, which fails without this
fix, and passes with the fix applied.

  FAIL: gdb.trace/pr16508.exp: interpreter-exec mi "-trace-find frame-number 0"

gdb:

2014-03-06  Yao Qi  <yao@codesourcery.com>

	PR breakpoints/16508
	* tracepoint.c (check_trace_running): New function.
	(trace_find_command): Move code to check_trace_running and
	call check_trace_running.
	(trace_find_pc_command): Likewise.
	(trace_find_tracepoint_command): Likewise.
	(trace_find_line_command): Likewise.
	(trace_find_range_command): Likewise.
	* tracepoint.h (check_trace_running): Likewise.
	* mi/mi-main.c (mi_cmd_trace_find): Call check_trace_running.

gdb/testsuite:

2014-03-06  Yao Qi  <yao@codesourcery.com>

	* gdb.trace/pr16508.exp: New file.