Merge branch '10.1' into 10.2

But without f4f48e06215..f8a800bec81 - fixes for MDEV-12672
and related issues. 10.2 specific fix follows...

sql/sql_class.h

@@ -1648,6 +1648,29 @@ public:
 };
 
 
+/**
+  Implements the trivial error handler which counts errors as they happen.
+*/
+
+class Counting_error_handler : public Internal_error_handler
+{
+public:
+  int errors;
+  bool handle_condition(THD *thd,
+                        uint sql_errno,
+                        const char* sqlstate,
+                        Sql_condition::enum_warning_level *level,
+                        const char* msg,
+                        Sql_condition ** cond_hdl)
+  {
+    if (*level == Sql_condition::WARN_LEVEL_ERROR)
+      errors++;
+    return false;
+  }
+  Counting_error_handler() : errors(0) {}
+};
+
+
 /**
   This class is an internal error handler implementation for
   DROP TABLE statements. The thing is that there may be warnings during