gdbserver: on GDB breakpoint reinsertion, also delete the breakpoint's commands.

If GDB decides to change the breakpoint's conditions or commands,
it'll reinsert the same breakpoint again, with the new options
attached, without deleting the previous breakpoint.  E.g.,

 (gdb) set breakpoint always-inserted on
 (gdb) b main if 0
 Breakpoint 1 at 0x400594: file foo.c, line 21.
 Sending packet: $Z0,400594,1;X3,220027#68...Packet received: OK
 (gdb) b main
 Breakpoint 15 at 0x400594: file foo.c, line 21.
 Sending packet: $Z0,400594,1#49...Packet received: OK

GDBserver understands this and deletes the breakpoint's previous
conditions.  But, it forgets to delete the previous commands.

gdb/gdbserver/
2014-06-02  Pedro Alves  <palves@redhat.com>

	* ax.c (gdb_free_agent_expr): New function.
	* ax.h (gdb_free_agent_expr): New declaration.
	* mem-break.c (delete_gdb_breakpoint_1): Also clear the commands
	list.
	(clear_breakpoint_conditions, clear_breakpoint_commands): Make
	static.
	(clear_breakpoint_conditions_and_commands): New function.
	* mem-break.h (clear_breakpoint_conditions): Delete declaration.
	(clear_breakpoint_conditions_and_commands): New declaration.
dprintf-style agent can't explain a trap.

If some event happens to trigger at the same address as a dprintf-style
agent dprintf is installed, GDB will complain, like:

 (gdb) continue
 Continuing.
 May only run agent-printf on the target
 (gdb)

Such dprintfs are completely handled on the target side, so they can't
explain a stop, but GDB is currently putting then on the bpstat chain
anyway, because they currently unconditionally use bkpt_breakpoint_hit
as breakpoint_hit method.

gdb/
2014-06-02  Pedro Alves  <palves@redhat.com>

	* breakpoint.c (dprintf_breakpoint_hit): New function.
	(initialize_breakpoint_ops): Install it as dprintf's
	breakpoint_hit method.
Installing a breakpoint on top of a dprintf makes GDB lose control.

While the full fix for PR 15180 isn't in, it's best if we at least
make sure that GDB doesn't lose control when a breakpoint is set at
the same address as a dprintf.

gdb/
2014-06-02  Pedro Alves  <palves@redhat.com>

	* breakpoint.c (build_target_command_list): Don't build a command
	list if we have any duplicate location that isn't a dprintf.

gdb/testsuite/
2014-06-02  Pedro Alves  <palves@redhat.com>

	* gdb.base/dprintf-bp-same-addr.c: New file.
	* gdb.base/dprintf-bp-same-addr.exp: New file.