GNATCOLL.Memory: Improve documentation of the Stack_Trace_Depth parameter

Setting this parameter to zero when calling the Configure procedure
has the effect of disabling completely the tracking of the biggest
memory users, which wasn't clear from the current documentation.
So this patch enhances the documentation of both the Configure
procedure as well as the Dump procedure to make that explicit.

Change-Id: Ib8c4733b9e821779cf52e5bfc892969fddea44b5
TN: V302-002

Author: brobecke

src/gnatcoll-memory.ads

@@ -1,7 +1,7 @@
 ------------------------------------------------------------------------------
 --                             G N A T C O L L                              --
 --                                                                          --
---                     Copyright (C) 2005-2019, AdaCore                     --
+--                     Copyright (C) 2005-2022, AdaCore                     --
 --                                                                          --
 -- This library is free software;  you can redistribute it and/or modify it --
 -- under terms of the  GNU General Public License  as published by the Free --
@@ -141,7 +141,8 @@ package GNATCOLL.Memory is
    --    traces that are output to indicate locations of actions for error
    --    conditions such as bad allocations. If set to zero, the debug pool
    --    will not try to compute backtraces. This is more efficient but gives
-   --    less information on problem locations
+   --    less information on problem locations (and in particular, this
+   --    disables the tracking of the biggest users of memory).
    --
    --    Maximum_Logically_Freed_Memory: maximum amount of memory (bytes)
    --    that should be kept before starting to physically deallocate some.
@@ -199,8 +200,12 @@ package GNATCOLL.Memory is
 
    procedure Dump (Size : Positive; Report : Report_Type := All_Reports);
    --  Dump information about memory usage.
-   --  Size is the number of the biggest memory users we want to show. Report
-   --  indicates which sorting order is used in the report
+   --  Size is the number of the biggest memory users we want to show
+   --  (requires that the Debug_Pool has been configured with Stack_Trace_Depth
+   --  greater than zero). Also, for efficiency reasons, tracebacks with
+   --  a memory allocation below 1_000 bytes are not shown in the "biggest
+   --  memory users" part of the report.
+   --  Report indicates which sorting order is used in the report.
 
    procedure Reset;
    --  Reset all internal data. This is in general not needed, unless you want