gdb/

gdb/
	* common/linux-procfs.c (linux_proc_get_int): New, from
	linux_proc_get_tgid, change its LWPID type to pid_t, add parameter
	field.
	(linux_proc_get_tgid): Only call linux_proc_get_int.
	(linux_proc_get_tracerpid): New.
	(linux_proc_pid_has_state): New, from linux_proc_pid_is_zombie.
	(linux_proc_pid_is_stopped, linux_proc_pid_is_zombie): Only call
	linux_proc_pid_has_state.
	* common/linux-procfs.h (linux_proc_get_tracerpid): New declaration.
	* common/linux-ptrace.c: Include linux-procfs.h and buffer.h.
	(linux_ptrace_attach_warnings): New.
	* common/linux-ptrace.h (struct buffer, linux_ptrace_attach_warnings):
	New declaration.
	* linux-nat.c: Include exceptions.h, linux-ptrace.h and buffer.h.
	(linux_nat_attach): New variables ex, buffer, message and message_s.
	Wrap to_attach by TRY_CATCH and call linux_ptrace_attach_warnings.

gdb/gdbserver/
	* linux-low.c (linux_attach_lwp_1): New variable buffer.  Call
	linux_ptrace_attach_warnings.

gdb/testsuite/
	* gdb.base/attach-twice.c: New files.
	* gdb.base/attach-twice.exp: New files.