Propagate exceptions fully when using proc_lib

This makes proc_lib behaves like a normal process as far
as the propagation of exceptions is concerned.

Before this commit, the following difference could be
observed:

  6> spawn_link(fun() -> ssl:send(a,b) end).
  <0.43.0>
  7> flush().
  Shell got {'EXIT',<0.43.0>,
             {function_clause,
              [{ssl,send,[a,b],[{file,"..."},{line,275}]}]}}
  ok

  8> proc_lib:spawn_link(fun() -> ssl:send(a,b) end).
  <0.46.0>
  9> flush().
  Shell got {'EXIT',<0.46.0>,function_clause}

After this commit, we get the following instead:

  3> flush().
  Shell got {'EXIT',<0.61.0>,
             {function_clause,
              [{ssl,send,[a,b],[{file,"..."},{line,275}]},
               {proc_lib,init_p,3,[{file,"..."},{line,232}]}]}}

The stacktrace will show minor differences of course
but the form is now the same as without proc_lib.

The rationale behind this commit is that:

* We now have a single form regardless of how the process
  was started

* We can use the stacktrace to programmatically alter behavior
  (for example an HTTP server identifying problems in input
  decoding to send back a generic 400, or a 500 otherwise)

* We can access the stacktrace to print it somewhere (for
  example an HTTP server could send it back to the client
  when a debug mode is enabled)

1 files changed, 28 insertions, 3 deletions

diff --git a/lib/stdlib/test/proc_lib_SUITE.erl b/lib/stdlib/test/proc_lib_SUITE.erl
index 416650e27e..a53e99afc9 100644
--- a/lib/stdlib/test/proc_lib_SUITE.erl
+++ b/lib/stdlib/test/proc_lib_SUITE.erl
@@ -26,7 +26,7 @@
 
 -export([all/0, suite/0,groups/0,init_per_suite/1, end_per_suite/1, 
 	 init_per_group/2,end_per_group/2, 
-	 crash/1, sync_start_nolink/1, sync_start_link/1,
+	 crash/1, stacktrace/1, sync_start_nolink/1, sync_start_link/1,
          spawn_opt/1, sp1/0, sp2/0, sp3/1, sp4/2, sp5/1,
 	 hibernate/1, stop/1, t_format/1]).
 -export([ otp_6345/1, init_dont_hang/1]).
@@ -50,7 +50,7 @@
 suite() -> [{ct_hooks,[ts_install_cth]}].
 
 all() -> 
-    [crash, {group, sync_start}, spawn_opt, hibernate,
+    [crash, stacktrace, {group, sync_start}, spawn_opt, hibernate,
      {group, tickets}, stop, t_format].
 
 groups() -> 
@@ -198,6 +198,31 @@ match_info(Tuple1, Tuple2) when tuple_size(Tuple1) =:= tuple_size(Tuple2) ->
 match_info(_, _) ->
     throw(no_match).
 
+stacktrace(Config) when is_list(Config) ->
+    process_flag(trap_exit, true),
+    %% Errors.
+    Pid1 = proc_lib:spawn_link(fun() -> 1 = 2 end),
+    receive
+	{'EXIT',Pid1,{{badmatch,2},_Stack1}} -> ok
+    after 500 ->
+	ct:fail(error)
+    end,
+    %% Exits.
+    Pid2 = proc_lib:spawn_link(fun() -> exit(bye) end),
+    receive
+	{'EXIT',Pid2,bye} -> ok
+    after 500 ->
+	ct:fail(exit)
+    end,
+    %% Throws.
+    Pid3 = proc_lib:spawn_link(fun() -> throw(ball) end),
+    receive
+	{'EXIT',Pid3,{{nocatch,ball},_Stack3}} -> ok
+    after 500 ->
+	ct:fail(throw)
+    end,
+    ok.
+
 sync_start_nolink(Config) when is_list(Config) ->
     _Pid = spawn_link(?MODULE, sp5, [self()]),
     receive
@@ -457,7 +482,7 @@ stop(_Config) ->
     %% System message is handled, but process dies with other reason
     %% than the given (in system_terminate/4 below)
     Pid5 = proc_lib:spawn(SysMsgProc),
-    {'EXIT',{badmatch,2}} = (catch proc_lib:stop(Pid5,crash,infinity)),
+    {'EXIT',{{badmatch,2},_Stacktrace}} = (catch proc_lib:stop(Pid5,crash,infinity)),
     false = erlang:is_process_alive(Pid5),
 
     %% Local registered name