Implement gdbsrv "v.info stats" command giving statistics for valgrind core + tools

* addition of VG_(needs_print_stats) in pub_tool_tooliface.h
* use the above in memcheck and helgrind
* output valgrind stats and calls print_stats in server.c



git-svn-id: svn://svn.valgrind.org/valgrind/trunk@13760 a5019735-40e9-0310-863c-91ae7b9d1cf9
diff --git a/gdbserver_tests/mchelp.stdoutB.exp b/gdbserver_tests/mchelp.stdoutB.exp
index c9b1729..7dfd0c3 100644
--- a/gdbserver_tests/mchelp.stdoutB.exp
+++ b/gdbserver_tests/mchelp.stdoutB.exp
@@ -62,6 +62,7 @@
      (with aspacemgr arg, also shows valgrind segments on log ouput)
   v.info exectxt          : show stacktraces and stats of all execontexts
   v.info scheduler        : show valgrind thread state and stacktrace
+  v.info stats            : show various valgrind and tool stats
   v.set debuglog <level>  : set valgrind debug log level to <level>
   v.translate <addr> [<traceflags>]  : debug translation of <addr> with <traceflags>
     (default traceflags 0b00100000 : show after instrumentation)