gdb/

Make core files the process_stratum.
	* corefile.c (core_target): New variable.
	(core_file_command): Remove variable t, use core_target.
	* corelow.c (core_ops): Make it static.
	(init_core_ops): Change to process_stratum.  Initialize CORE_TARGET.
	* defs.h (make_cleanup_unpush_target): New prototype.
	* gdbarch.h: Regenerate.
	* gdbarch.sh (core_pid_to_str): Remove core_stratum from its comment.
	* gdbcore.h (core_target): New declaration.
	* inf-ptrace.c (inf_ptrace_create_inferior, inf_ptrace_attach): New
	variables ops_already_pushed and back_to.  Use push_target,
	make_cleanup_unpush_target and discard_cleanups calls.
	* record.c (record_open): Replace core_stratum by a core_bfd check.
	* target.c (target_is_pushed): New function.
	(find_core_target): Remove.
	* target.h (enum strata) <core_stratum>: Remove.
	(target_is_pushed): New declaration.
	(find_core_target): Remove declaration.
	* tracepoint.c (init_tfile_ops) <to_stratum>: Remove comment.
	* utils.c (do_unpush_target, make_cleanup_unpush_target): New functions.

gdb/doc/
	Make core files the process_stratum.
	* gdb.texinfo (Active Targets): Remove core_stratum.  Include
	record_stratum example.

gdb/testsuite/
	Make core files the process_stratum.
	* gdb.base/corefile.exp (run: load core again)
	(run: sanity check we see the core file, run: with core)
	(run: core file is cleared, attach: load core again)
	(attach: sanity check we see the core file, attach: with core)
	(attach: core file is cleared): New tests.
	* gdb.base/coremaker.c (main): New parameters.  Implement "sleep" argv.

gdb/testsuite/gdb.base/coremaker.c

@@ -133,8 +133,14 @@ func1 ()
   func2 ();
 }
 
-int main ()
+int
+main (int argc, char **argv)
 {
+  if (argc == 2 && strcmp (argv[1], "sleep") == 0)
+    {
+      sleep (60);
+      return 0;
+    }
   mmapdata ();
   func1 ();
   return 0;