linux-procfs: Handle lowercase "t (tracing stop)" state

linux-procfs: Handle lowercase "t (tracing stop)" state

Since Linux 2.6.33, /proc/PID/status shows "t (tracing stop)", with
lowercase 't'.  Because GDB is only expecting "T (tracing stop)", GDB
can incorrectly suppress errors in check_ptrace_stopped_lwp_gone:

 1578          if (!check_ptrace_stopped_lwp_gone (lp))
 1579            throw_exception (ex);

Ref: https://sourceware.org/ml/gdb-patches/2016-06/msg00072.html

2016-07-25  Pedro Alves  <palves@redhat.com>
	    Jan Kratochvil  <jan.kratochvil@redhat.com>

	* nat/linux-procfs.c (parse_proc_status_state): Handle lowercase
	't'.