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.