Hi,

This issue is because GDB doesn't OP_STRING now.  So
parse_cmd_to_aexpr will got NULL if using agent dprintf, %s format,
and an in-line string.
And this NULL will be push to bl->target_info.tcommands.  Then it make
remote part crash.

So add a check in build_target_command_list for the return of
parse_cmd_to_aexpr.  And add a test for it.

Thanks,
Hui

2013-05-11  Hui Zhu  <hui@codesourcery.com>

	PR gdb/15433
	* breakpoint.c (build_target_command_list): Add check for
	the return of parse_cmd_to_aexpr.

2013-05-11  Hui Zhu  <hui@codesourcery.com>

	PR gdb/15433
	* gdb.base/dprintf.exp: Test unsupport commands on target.