gdb/testsuite/

	* gdb.trace/read-memory.c: New.
	* gdb.trace/read-memory.exp: New.
gdb/

	* target.c (update_current_target): Change the default action
	of 'to_traceframe_info' from tcomplain to return_zero.
	* target.h (struct target_ops) <to_traceframe_info>: Add more
	comments.
	* valops.c (read_value_memory): Call
	traceframe_available_memory unconditionally.

gdb/testsuite/

	* gdb.trace/read-memory.exp (test_from_remote): Update test.
	(teset_from_exec): Likewise.